Key words
climate change - greenhouse gas emission - temperature - endocrine disrupting chemicals - brown fat - metabolic rate - COVID-19 - thermogenesis, obesity
Introduction
Obesity, a global pandemic, represents a major health challenge with individuals
affected with a weight stigma being less likely to receive adequate care [1]
[2].
Conversely, excellent patient awareness of obesity as a health problem but
misperception of obese status and unawareness about body mass index is high in
certain ethnic groups [3]
[4]. Obesity affects more than 680 million
adults worldwide and is present in nearly 40% of U.S. adults with
61% of patients diagnosed with diabetes mellitus being obese. Worldwide,
obesity has nearly tripled since 1975 and most of the world’s population
live in countries where overweight and obesity kills more people than underweight
[5]. Obesity is associated with risk of
various malignancies including breast and endometrial cancers, cancer of the
esophagus, gastric cardia, colon, rectum, liver, gallbladder, pancreas, kidney,
thyroid gland, and multiple myeloma [6]
[7]. [Figure
1] demonstrates the age-adjusted trends in overweight, obesity, and severe
obesity among men and women from age 20 to 74 years in the United States,
1960–1962 through 2017–2018 [8].
Fig. 1 Age-adjusted trends in overweight, obesity, and severe obesity
among men and women aged 20–74: United States, 1960–1962
through 2017–2018.
In 1856, Eunice Newton Foote (1819–1888) first reported that changing the
proportion of carbon dioxide in the atmosphere would change its temperature [9]. The most abundant greenhouse gases in
Earth’s atmosphere are water vapor, carbon dioxide (CO2),
methane, nitrous oxide, ozone, and fluorinated gases including chlorofluorocarbons
and hydrofluorocarbons [10].
The United States Environmental Protection Agency published global greenhouse gas
emissions by gas ([Fig. 2]
). These emissions are produced from using electricity generated from oil, natural
gas, and coal, burning oil or gas for home heating, or from burning gasoline when
driving vehicles ([Fig. 3a, b]) [11]. Deforestation has released and will
continue to release carbon dioxide and has become a major problem worldwide.
Fig. 2 Global greenhouse gas emissions by gas. (source: https://
www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data).
Fig. 3
a: Modern global CO2 emissions from the burning of fossil fuels.
(https://en.wikipedia.org/wiki/Greenhouse_gas_emissions);
b: 2016 Global greenhouse gas emissions by economy sector. Percentages are
calculated from estimated global emissions of all Kyoto greenhouse gases, converted to
CO2 equivalent quantities (GtCO2e). GHG: Greenhouse gas.
(source:
https://en.wikipedia.org/wiki/Greenhouse_gas_emissions;
http://earthcharts.org/category/climate-change/).
The main source of anthropogenic methane emissions is agriculture, for instance,
ruminant livestock such as sheep and cows, and anaerobic decomposition of organic
material in flooded rice paddies. The atmospheric concentration of CO2
has dramatically increased since the beginning of the Industrial Revolution, from
280 part per million in 1750 to 415 ppm in 2019 with approximately 90 ppm occurring
within the last 56 years [11]
[12].
Among the top ten emitting countries accounting for approx. 70% of the
world’s annual energy-related carbon CO2 emissions are China, the
United States, India, Russia, Japan, Germany, South Korea, Iran, Canada, and Saudi
Arabia.
In 2019, the EAT-Lancet commission published an extensive paper and first full
scientific review on the definition of healthy diets from sustainable food systems
and on which actions are able to support and accelerate food system transformation
in the current time and geological epoch, named the Anthropocene [13]. This detailed report starts with an
executive summary stating that 820 million people are not having sufficient or
high-quality food which contributes to the rising incidence of diet-related obesity.
The authors of this paper concluded that there is strong evidence
“indicating that food production is among the largest drivers of global
environmental change by contributing to climate change, biodiversity loss,
freshwater use, interference with the global nitrogen and phosphorus cycles, and
land-system change and chemical pollution.” As of now, the global population
is estimated at 8 billion people and predicted to grow to 10 billion by 2050 [13]
[14].
To what extent the growth and number of the world population will be affected by
future pandemics such as the Covid-19 pandemic is uncertain [15]
[16]
[17].
In this article we review the bidirectional interaction between climate
change/global warming and human metabolism/adiposity.
Economics
The relationship between economic growth and environmental degradation is shown in
the environmental Kutznets curve (EKC). The EKC hypothesis presents a bell-curved
relationship between economic growth and CO2 emissions and its validity
in the context of Vietnam has recently been studied [18]. In that study, Vo and Ho utilized the auto-regressive distributed
lags (ARDL) model to investigate both short-term and long-term relationships between
variables and grouped different energy consumption types into two main categories:
a) fossil energy consumption including coal, gas, and oil consumption, and b)
renewable energy consumption including hydroelectric consumption for which Vietnam
seems to be suited given its massive network of rivers and major lakes. The authors
also performed a threshold regression to determine the per capita gross domestic
product level. Several studies examining the validity of the EKC hypothesis conclude
that CO2 emissions will increase as income increases to a certain level.
Aslan et al. [19] found that the effect of
economic growth on CO2 emissions in the United States of America was
increasing from 1982 to 1996 and decreasing from 1996 to 2013. In Vietnam,
CO2 emissions have increased approximately ten times while economic
growth has increased five times from 1986 to 2018 [18]. Energy consumption has tremendously increased, 14 times by fossil
sources and more than 50 times by renewable energy sources [18]. The annual economic growth rate has been
maintained above 5% since 1988, principally supported by foreign direct
investment which seems to improve environmental quality at the lower threshold of
economic growth and in the short-run. An increase in foreign direct investment and
consumption of fossil fuel energy deteriorates the environment in the long run at
any level of economic growth in Vietnam. The authors Vo and Ho believe that this
data can also be useful for other developing and emerging markets.
Possible Effects of Global Warming on Adiposity
Possible Effects of Global Warming on Adiposity
It is believed that the effects of food production on emissions of CO2,
methane, nitrous oxide, and ozone, referred to as primary greenhouse gases in the
atmosphere of the planet Earth, will reduce the stability of the Earth system. The
first systematic review on the relationship between global warming and the obesity
epidemic, including 50 studies published in or after 2002 attempted to find answers
for the questions whether global warming and the obesity epidemic share common
determinants, whether one influences the other and/or each other, and which
pathways would underlie such a relationship [20]. The authors of this review constructed a conceptual model linking
global warming and the obesity epidemic: a) Land use, urbanization, motorized
transportation and agricultural productivity which is affected by population growth,
industrialization and the fossil fuel economy, b) These factors influence global
warming by excess greenhouse gas emission and impact the obesity epidemic by
nutrition transition and physical inactivity, c) global warming directly affects
obesity by food supply/price shock and adaptive thermogenesis, and d. the
obesity epidemic contributes to global warming by elevated energy consumption.
Kanaszawa [21] argues that endotherms acquire
more calories by eating food at a higher temperature than eating the identical food
cold and that atmospheric temperature correlates with small increases in weight
based on an analysis of the National Longitudinal Study of Adolescent to Adult
Health.
Fat Tissue and Thermogenesis
Fat Tissue and Thermogenesis
As reviewed in Turner et al. [22], obese men
typically have the largest adipose tissue thickness in the abdominal region, whereas
obese women accumulate excessive fat at the femoral and gluteal regions [23]. Initial fat cell weight enlargement (up to
0.8 μg per cell in each region) is followed by an increased fat cell
number [23]. Figurines of women with obesity
from Upper Paleolithic Europe rank amongst the earliest art and may relate to human
adaptation to climate change, as during this time period from 38 000 to 14 000
before present, humans faced advancing glaciers and falling temperatures leading to
nutritional stress and a reduction in the population [24].
Obesity may be associated with 20% greater emissions from greenhouse gases
compared with the normal weight state. This is the result from oxidative metabolism
due to greater metabolic demands, from food production processes due to increased
food intake, and from automobile and air transportation due to greater body weight
[25].
Energy balance is a key concept in developing strategies to fight obesity. This
balance is affected by calorie intake, physical activity and by energy dissipation
[26].
Physical activity/exercise includes endurance and resistance training, both
leading to adaptive changes in skeletal muscle and production and secretion of
myokines including irisin which besides myogenesis can switch white adipocytes to
brown fat-like cells, causing an increase in energy expenditure [27]
[28]
[29]. Short-term metformin
treatment does not change brown adipose tissue (BAT) activity in women with
polycystic ovarian syndrome [30].
Obesity can be promoted by impaired thermogenesis, for instance, by decreased
expression of thermogenesis related genes encoding uncoupling proteins, thyroid
hormone receptors, beta adrenergic receptors, and 5′-iodothyroxine
deiodinases [31]. Bisphenol A, a chemical
produced in large quantities of polycarbonate plastics and epoxy resins and found in
food and drink packaging, is an endocrine disrupting chemical which can affect the
metabolism of thyroid hormone by inhibiting type 1 iodothyronine deiodinase [32].
Adaptive thermogenesis is defined as the complex response of homoeothermic organisms
to increase the rate of energy expenditure above normal baseline levels during
exposure to cold in order to maintain core temperature [33].
The adaptive thermogenesis response shows large inter-individual variability. With
cold exposure, South Asians showed lower resting energy expenditure, non-shivering
thermogenesis, and brown adipose tissue volumes compared to Caucasians [34].
The process of thermogenesis in which brown or beige adipocytes contribute to
increased energy expenditure is not fully functional in all populations. Studies
have shown that increased time spent in a thermal neutral zone (the range of ambient
temperatures at which the metabolic rate is minimal) can lead to a loss of brown
adipose tissue and reduced thermogenic capacity (reviewed by Johnson et al. [35]). With the advancements of central heating
and air conditioning in homes, transportation and businesses, a cultural shift in
ambient temperature exposure towards that of thermal comfort has occurred. While
specific data on indoor temperatures varies with different collecting strategies and
protocols, the overall upward trend of indoor temperatures during the winter months
is prevalent [36]
[37]. People are spending less time exposed to
temperature extremes and more time in temperature-controlled
“comfortable” environments.
Thermogenesis makes up about 10% of total energy expenditure which plateaus
above moderate physical activity levels [38].
Diet-induced thermogenesis is determined by the diet consumed. Energy released in
form of heat is the lowest for fat (2%), followed by glucose (8%),
protein (20–30%), and alcohol (22%) with large
inter-individual variability determined by genetic factors, gender, various hormones
and the sympathetic nervous system activity [37]. Thyroid hormone regulates the basal metabolic rate and energy
expenditure. Cold-induced thermogenesis is higher in euthyroid compared to
hypothyroid individuals [39].
Ambient temperature exposure thus plays an important role in BAT activity. As the
thermogenic activity of BAT is stimulated by cold exposure, more time spent in the
thermal comfort zone will lead to loss of BAT activity, thereby decreasing energy
expenditure with potential obesogenic consequences. Brown adipose tissue plays a
role in the development and treatment of nonalcoholic steatohepatitis, a liver
condition which can promote the chronic inflammatory state in obese individuals
[40].
Overweight and obese adults are at greater risk for heat-related illness or injury
[41]. Obese older adults were twice as
likely to die during the 2003 European heatwave compared to non-obese individuals
[42]. Heatstroke occurs much more
frequently in obese or overweight people compared to normal weight individuals
because of reduced ability to dissipate heat [41]
[43]
[44].
Elevated air pollution with ambient particulate matter 2.5 contributes to climate
change and is linked to reduced physical activity [45].
Climate Change
At the current emission rates, the United Nations’ Intergovernmental Panel on
Climate Change (IPCC) estimated that temperatures could increase by 2°C by
2036. In Germany where two of the authors of this article were born, weather
documentations since 1881 indicate that the air temperature increased by
1.5°C in 2020 in Germany ([Fig. 4]),
while it increased globally by 1°C. Since the year 2000, sea levels are
rising, and the number of extreme weather events has increased including prolonged
heat waves and flood rains.
Fig. 4 German climate atlas (source:
www.dwd.de).
Climate experts in Germany estimate summer temperatures to be as hot as 45°C
by the year 2100 with a desert landscape in many German regions similar to the area
around Dabuleni in Southern Romania, if the Paris Agreement will not be met
(Klimawandel. Die Fakten mit Harald Lesch. ZDFzeit 28.2.2021 und 21.10.2020). This
agreement represents a legally binding international treaty on climate change and
was entered into force in November 2016. Its goal is to keep the increase of global
mean temperature to below 2 °C, compared to pre-industrial levels [46]. Since 1950 the number of dry soil areas
and droughts in Germany have increased with an approximate water deficit of 500
liters per square meter. The rapeseed harvest in Brandenburg, Germany, has declined
by 20% because of increasing droughts. The reason for these extreme weather
events, not only in Germany but also in the United States and other regions of the
world, is a weather pattern called omega block. Deforestation aggravates this
problem. Although 32% of Germany is covered with forest, 40% of that
forest is badly damaged leading to forest dieback. Trees can bind 14% of
greenhouse gas emissions (CO2) and enable the soil to keep water and
moisture. Water deprivation of especially spruce trees make them prone to become
infested with the bark beetle, which then further promotes forest dieback. In 2018,
the level of the Elbe river near Dresden measured only 18 cm and the level
of the Rhine river near Emmerich 7 cm, making such main waterways impassable
for shipping, thereby leading to a transportation problem of major goods [47].
The Baltic Sea water temperature is now 1.9% warmer in 20 meter depth than in
1980. Concomitantly there is a rise of dead herring and overall reduction of the
Baltic Sea herring number which will change the food chain over time. The North Sea
water temperature has increased by 1.3°C during the twentieth century and
the water level at Pellworm (Germany) has risen by 25 cm. Along with rising
sea levels there is a retreat of glaciers since 1850. In the Alps, the ensuing lack
of glacier water can lead to reduction of drinking water. Indeed in summer 2020,
there was a shocking shortage of drinking water in Lauenau, Germany. In Helgoland,
the technique of reverse osmosis is utilized to obtain drinking water under high
energy consumption.
Hard evidence for the irrefutable fact that global warming and climate change exist
is the recent break/ice calving of iceberg A-68, that one might call the
“tipping point” of climate change [48]. This giant iceberg with a surface area of 5800 square kilometers
(2200 square miles) and an estimated weight of one trillion tones, broke
up/off from the Larsen C ice shelf in Antarctica on July 12, 2017. However,
this did not happen suddenly, as scientists identified the start of the ice cracking
in November 2016, forming a lace-network of cracks. Since 1940 the air temperature
in Antarctica rose by 0.5 °C every 10 years to a total of 4 °C now.
Continental ice pressures shelf ice leading to an increase in energy and
temperature. With an increase in air temperature, an increase in water temperature
occurs and ice will melt. Via satellites, radar, and infrared cameras, it has become
possible to watch the ice moving following the Bernoulli principle which states that
an increase in the speed of a liquid happens simultaneously with a decrease in
static pressure or a reduction in the fluid’s potential energy. Satellite
images from the European Space Agency show the iceberg A-68 moving towards South
Georgia Island and that it has broken up in major fragments in December 2020.
It is obvious that such events contribute to rising sea levels. Furthermore,
“Atlantification” of the Arctic promotes rising sea levels and is
characterized by warmer ocean temperatures and a reduced sea ice cover, currently
well observed at the Barents Sea [49]. In the
Arctic, the East Siberian and Laptev Sea harbor methane deposits. Arctic warming by
a few degrees Celsius may lead to permafrost thawing, coastal erosion, and the
release of methane and CO2 into the atmosphere, likely further worsening
global warming [50].
Potential Solutions to Remove Greenhouse Gases from the Atmosphere
Potential Solutions to Remove Greenhouse Gases from the Atmosphere
On an individual level, one should learn more about how to contribute to less
consumption of energy generating CO2 and other greenhouse gas emissions.
This could include forcing construction companies to higher standards regarding the
insulation of residences and homes using material that demonstrates the best
protection against heat and cold, particular as an estimated 6% of global
greenhouse gas emissions derive from buildings. Exemplary spending less time in the
thermal comfort zone could contribute both to decrease CO2 emissions and
potentially affect obesity as well.
Transportation which accounts for 14% of the global greenhouse gas emissions
is a valuable target for each of us willing to help decrease CO2
emissions for instance by bicycling, walking, or taking stairs instead of elevators,
and taking the bus or car pool [51]. This is a
major challenge for urban designers [52].
Considering that an electric car with a battery of 40 kWh (kilowatt hour) has to
drive 72 000 km (45 000 miles) and one with a battery of 95 kWh drives 166
000 km (103 000 miles) to achieve an advantage regarding carbon dioxide
emissions towards a car that uses gasoline, adding the environmental damage caused
by the raw material used for the battery versus the raw material (steel, fiberglass)
used for a traditional car, there does not seem to be an ecological advantage to
increasingly use electric cars to help the climate change [53]
[54].
On a community level, green/plant areas should be increased to help absorb
CO2 via photosynthesis and improve the air quality, as well as combat
extreme weather conditions with flood rains and episodes of drought and heat. The
largest “green façade” project in Europe was completed in
2020 in Düsseldorf, Germany, with hornbeams and other plants covering the
roofs of major buildings and providing some cooling in hot summer days when heat
increases in the city because of concrete and little wind flow [55]. This is part of the climate change concept
called “sponge city” with the idea to return back to the future of
having ditches instead of canalization/sewerage several hundred years ago.
However, this new urban construction model aims at flood management and urban heat
problems. Rain water should be captured and repurposed for irrigation [56].
The Covid-19 pandemic showed clearly how humans contribute to the production of
greenhouse gases. This pandemic,which dramatically impacted all of our lives, also
had substantial impact on the economy, transportation, production in any sector,
etc. and resulted in an estimated 17% decrease of daily global
CO2 emissions when comparing April 2019 with April 2020 [57]. The COVID-19 pandemic showed how much
humans contribute to and could positively impact greenhouse gas emissions.
Stopping deforestation and instead planting more trees to obtain a mixed forest
(consisting of spruce,douglasie trees and also deciduous trees) can help to not only
bind CO2, but also promote humus growth/development and act as a
sponge that stores water. This may require reducing cattle ranching which often has
the goal to export meat and drives further deforestation for soybean production
fields. Another reason for deforestation is logging and the economic opportunity to
export timber, in part used as charcoal. In the Amazon’s tropical
rainforest, deforestation has led to loss of biodiversity and threat of
desertification [58].
In Scotland known for its moorland in the Scottish Highlands, sphagnum, commonly
called peat moss, can store water and carbon. Therefore, this type of moss in
climate terms is classified as being “CO2 neutral”.
Notable moorlands exist in Africa, Alaska, Europe, Russia, North and South America
[59].
Drainage of the moors/swamps should be stopped and, instead, the focus should
be to enrich these regions with water/“re-water” them. When
air instead of water enters the soil of the moor/swamp, an aerob
mineralization of organic substances in the moor soil takes place and it no longer
serves as a carbon storage.
Agroforestry utilizes trees and shrubs that are grown around or among crops or
pastureland. This could serve as windbreaker. Other practices include Riparian
forest buffers, forest farming, alley cropping, and silvopasture [60].
In terms of forests, the last word, however, has not been spoken. Canadian forests,
for example, were net emitters of CO2 in 2017 and 2018 due to wildfires
and several practices such as slash burning [61]. This delineates the importance of planting new trees, maintaining
forests, keeping them “healthy” and addressing outbreaks like the
pine beetle which impact indirectly CO2 emissions. Wood will remain an
important natural product in our daily lives and sustainability of wooden products
must be paramount to us.
Carbon capture and storage (CCS) can reduce greenhouse gas emission rates [62]. This can be accomplished by removing
CO2 from the atmosphere under high pressure into geologic formations
such as depleted oil and gas reservoirs, unmineable coal seams, and deep saline
reservoirs, or into the soil. Impermeable cap rock typically prevents the
CO2 from leaking back to the surface. Deep ocean storage could
acidify the ocean. When CCS is combined with biomass it can result in net negative
emissions. At present, the two largest-scale power plants with CCS are Petra Nova
Carbon Capture in the United States and Boundary Dam CCS in Canada. Natural gas
power stations usually emit less CO2 than coal-fired power plants. CCS
can capture more than 800 000 tons of CO2 per year at a large coal-fired
power plant. In the United Kingdom, one ton of CO2 from the atmosphere
could be removed by the Drax power station in North Yorkshire, England, in 2019. In
Norway, depleted oil and gas reservoirs are considered for CCS and scientists from
all over the world are searching for regions to deploy CCS technology offshore. The
Northern Lights initiative, supported by the Norwegian government, the French
multinational integrated oil and gas company Total SE, the energy company Equinor
ASA, and the Royal Dutch Shell PLC, intends to store 1.5 million tons of
CO2 per year under the North Sea starting in 2024 [63]. In Japan under the CCS demonstration
project in Tomakomai city, the Ministry of Economy, Trade and Industry, injected 300
000 tons of CO2 underground in November 2019 [64].
In Iceland, known for its volcanoes, CCS has been adapted for the black basalt rock.
CO2 released from manufacturing plant smokestacks is captured and
injected into the Icelandic basalt rock in approximately 500 m depth. The
typical CCS procedure would separate CO2 from other gases, transport it
via pipeline or ship to a suitable site, and then inject it deep underground where
it turns into carbonate material such as calcite known as component of marble and
limestone (based on sufficient amounts of calcium, magnesium, iron). In Iceland, the
adapted CCS method is called CarbFix which involves dissolving CO2 in
water before or during injecting it into the porous basalt rock. This makes
CO2 less buoyant allowing it to sink down through the rock and
reducing the risk of CO2 escape into the atmosphere. Mineralization of
CO2 is facilitated by higher temperatures with 20 – 50
°C typically being sufficient for rapid mineralization. Volcanic Iceland has
many high temperature zones with underground temperature reaching 250 °C
within 1 kilometer depth. In low temperature zones, the temperature still reaches up
to 150 °C within 1 kilometer depth [65].
Endocrine Disruption
Global warming impacts ecosystems. Yacine et al. [66] investigated simulated trophic networks of co-evolving consumers to
warming under different evolutionary scenarios and concluded that the long term
diversity loss triggered by warming is higher in scenarios where evolution is slowed
down or switched off, suggesting that eco-evolutionary feedback helps preserve
biodiversity. The authors warn that reversing warming may not be sufficient to
restore previous structures. Climate change with altered temperatures can cause
endocrine disruption in humans and in animals [67] ([Fig. 5]).
Fig. 5 Transmission and distribution of environmental endocrine disruptors in the
ecosystem and food chain.
Food contact plastics, some pesticides, flame retardants, perfluorinated compounds,
and other endocrine disrupting chemicals (EDC) are derived from oil, coal, or gas
[68]
[69]. Rising temperatures during climate change likely impact insect
populations. Pesticide use significantly contributes to biodiversity loss [70], acknowledging that the use of pesticides
and fertilizers combined with deforestation are the main drivers of biodiversity
loss. Many EDCs are lipophilic, can promote adipogenesis, and cause weight gain and
tumor growth [5]
[71].
Endothermic animals, which need to maintain a constant internal body temperature for
optimal metabolic function face a crucial challenge due to the necessity of complex
thermoregulatory mechanisms. Several endocrine changes occur when an endothermic
animal adapts to hot temperatures. Neuroendocrine mechanisms reduce food intake and
metabolism in hot environment. This leads to reduced thyroid activity, reduced
testosterone production, and the cortisol production initially increases and then
decreases upon prolonged heat exposure [72].
On the contrary, cold temperatures cause elevations in adrenal steroidal hormones,
and increase the activity in pituitary and thyroid glands. Prolonged cold exposure
can cause thyroid and adrenal gland hypertrophy [72]. Experiments on quails, finch, and other bird species have
demonstrated that thermal adaptation varies across species of endotherms [73]. Facultative hyperthermia also results in
different incubatory and belly-soaking behaviors among different avian species [73]. Among mammals living in hot sub-tropical
deserts, the thermoregulation depends on a combination of surrounding temperature
and circadian cycles [73]. In general,
migratory or nomadic animals tend to possess narrow temperature tolerance, while
sedentary or non-migratory animals tend to better tolerate wider fluctuations in
temperature [73]. Therefore, climate change
can likely have a significant impact on the survival of migratory species. In
addition, climate change and thermal fluctuations can also change parasite biology
and parasite establishment, development, growth, and fecundity within their
endothermic hosts [72].
Climate change can act synergistically with EDCs in creating endocrine disruption.
There is growing concern for Arctic wildlife to inadequately adapt to changing
climate due to damage inflicted by EDCs, especially on the thyroid, sex steroid, and
glucocorticoid hormonal pathways [74]. In
humans, knowledge of the impact of climate change on obesity and various endocrine
systems is constantly evolving [22]
[75].
An expert panel, charged with the task to quantify a range of health and economic
costs that can be reasonably attributed to EDC exposures in the European Union,
achieved consensus at least for probable (>20%) EDC causation for
childhood obesity, obesity, adult diabetes mellitus, and other disorders which are
associated with costs in the hundreds of billions of Euros per year [76].
A big concern is the effect of changing global temperatures and their potential
catastrophic impact on altering endocrine functions of flora and fauna on a global
scale. Temperature increase, along with eutrophication in water bodies can increase
metabolic demand in aquatic life and accelerated metabolic rates, thus resulting in
hypoxic zones in the aquatic environment and further production of CO2
[77]. Elevated temperatures (to
30oC), along with decreased pH, and decreased water salinity delays
growth in Pacific oysters (Crassostrea gigas). Variations in temperature have
shown to cause differential effects in the body growth and gonadal size in tropical
sea urchins (Tripneustes gratilla), with warming ocean temperatures
increasing the susceptibility to disease and mortality among several species of sea
urchins [78]. Water bodies harbor most of the
life on the planet, with estimates of ~80% of life on Earth thriving
in the oceans. Change in the pH of water bodies, no doubt, will create a substantial
impact on aquatic and terrestrial life, global carbon-cycle and in turn, the
climate. A major effect of changes in pH is the acidification of the ocean. The
devastating consequences of ocean acidification have been evident even from
prehistoric times, and have been postulated to have contributed to mass extinctions,
especially the infamous late-Cretaceous mass extinction from the Chicxulub meteor
impact that wiped out a substantial amount of life on Earth, including the non-avian
dinosaurs and several marine invertebrate and vertebrate species [79]. Climate change and ocean acidification
often go hand-in-hand in causing major, or even catastrophic effects on
biodiversity. This is because of the propensity of increasing CO2 levels
in the atmosphere to cause a shift in the CO2-HCO3 equilibrium
towards the acidic direction [77]. Changes in
pH can also affect the dissociation status of endocrine disrupting chemicals, many
of which happen to be weak acids/bases [77]. In addition, the concentrations of various metal ions can be
affected by ocean acidification, which in turn can result in endocrine disruption
[77]. Another major effect of pH changes
and ocean acidification is its impact on water oxygenation levels. Deficiency or
excess in water oxygenation can give rise to ROS which can exert toxic effects on
the body, and on the endocrine system [77].
Low pH-mediated decrease in calcium carbonate mineral saturation can impair adequate
tissue calcification and growth [78]. Low pH
and low temperatures have been shown to reduce the success of fertilization,
embryonic development, and size of the larvae and increase abnormal larval
morphology in Sydney rock oyster (Saccostrea glomerate) and C.gigas.
[80]
. Similarly, low pH and
acidification has also shown to reduce gonadal and body growth in T.gratilla
[78]. Although data on the effects of
pH on vertebrate animals and humans is sparse, future studies can potentially shed
more light on this topic.
Acid rains are caused due to oxides of sulfur, nitrogen, and ozone, which
predominantly originate from the combustion of fossil fuel [81]. Acid rains can lower the pH of water
bodies, and this has resulted in a drop in populations of amphibians, molluscs, and
phytoplankton [81]. Similarly, on terrestrial
landscapes, acid rains have adversely affected the environment. Apart from altering
the growth and physiology of trees and crop plants, acid rains can indirectly affect
human health through liberation of toxic metals such as cadmium, lead, tin, mercury,
aluminum, iron, and manganese [81]. These
metals could seep into ground water, which is consumed by humans, that could
potentially lead to various endocrine abnormalities. Effects of acid rain on human
health is an important area for further research.
Obesity and Global Warming during the COVID-19 Pandemic
Obesity and Global Warming during the COVID-19 Pandemic
The emergence and spread of SARS-CoV2 appears to be related to urbanization, habitat
destruction, live animal trade, intensive livestock farming and global travel [82]. As of December 2020, CO2
emissions have declined in the year 2020 by 7% during the Covid-19 pandemic
([Fig. 6a, b]) [83]
[84].
Fig. 6
a: Carbon emissions; b: Carbon emission trend during Covid-19 pandemic.
* Megatonnes of carbon dioxide. 1. China imposes lockdown on Wuhan, where
coronavirus was first detected 2. Slammed by COVID, Italy issues a national lockdown 3.
California becomes first US state to impose lockdown 4. India begins its first
nationwide lockdown 5. As Europe surpasses 100 000 new daily infections, countries
announce new wave of restrictions 6. California imposes a 3-week lockdown after
registering its highest daily total of new infections.
The COVID-19 pandemic was shown to be associated with weight gain amongst adults and
children in most countries. One of the interventions to prevent the spread of this
potentially fatal virus has been to promote social distancing. This has been
achieved by various stay at home orders from governmental agencies, one of them
including school closures [85]. This
intervention may increase risk of childhood obesity which is associated with various
short and long-term illnesses like diabetes mellitus, hypertension, heart disease,
stroke and certain cancers [86]
[87]. Individuals with endocrine conditions are
disproportionately affected by COVID-19 [88]
[89]. A recent systematic review
and meta-analysis found that obesity is independently associated with an unfavorable
outcome of COVID-19 illness with a 50% increased risk of death [90].
The shutdown of our social environments like work or school, reduced physical
activity and the excess of free time during self-quarantine resulted in lifestyle
changes and changes of our eating habits. Changes in the sleep pattern, excessive
snacking, lack of diet restrictions, etc. were shown to be associated with weight
gain during the COVID-19 pandemic [91].
Although no studies addressed metabolic changes of weight gain focusing on the
COVID-19 pandemic, one can speculate that they remain unchanged compared to the time
prior to COVID-19. This dilemma can be tackled by an international modern training
program in diabetes and metabolism such as the TransCampus metabolic training
program in Dresden, Germany [92].
To reduce the risk of childhood obesity, the Physical Activity guidelines for
Americans recommends 60 minutes or more of moderate-to-vigorous physical
activity (MVPA) daily among children given physical inactivity is the major
behavioral risk factor for obesity in children [93]. However, school closures, stay at home orders, parks and outdoor
recreational activities closures thus have promoted an environment favoring obesity
[94]. Children in recent times have been
at high risk for energy imbalance and unhealthy weight gain [95]. To study the estimated impact of COVID-19
on childhood obesity, An studied this using a microsimulation model which showed an
increase in mean body mass due to physical inactivity in kids [96]. Increasing the fitness level and keeping
the body mass index at least stable are strategic initial goals for obese children
[97].
Possible Effects of Adiposity on Global Warming
Possible Effects of Adiposity on Global Warming
Swinburn et al. provide a detailed report including comparisons of the prevalence of
female obesity rates and the carbon footprint (greenhouse gas emissions in tons per
capita per year) between various regions of the world [75]. South Asia has a prevalence of female
obesity of 5% and a carbon footprint of 2.2, whereas high-income
English-speaking countries have a prevalence of female obesity of 33% and a
carbon footprint of 18.5 [75].
Although there is debate whether eating four pounds of beef equals the emissions of a
transatlantic flight and whether consuming a plant-based burger such as the start-up
“Impossible Burger” instead will help solve climate change [98]
[99]
[100]. This start-up is made
mainly of soy and potato proteins as well as coconut and sunflower oils [100]. A recent systematic review and
meta-analysis of cohort studies concluded that an intake reduction of 3 servings of
unprocessed or processed meat per week was associated with a very small reduction in
overall cancer mortality over a lifetime [101]. Such a reduction of consumption of processed and unprocessed meat was
also found to be associated with a very small reduction in risk for cardiovascular
mortality, stroke, myocardial infarction, and type 2 diabetes [102]
[103], the latter known to be also linked to obesity. Based on several such
systematic reviews a nutritional recommendations consortium suggested that adults
continue current unprocessed and processed meat consumption [104]. Agriculture land is used for livestock
grazing and 33 percent of croplands are used to grow feed for livestock. According
to data from the Environmental Protection Agency, livestock contributes to
9.3% of global greenhouse gas emissions [105].
The bidirectional relationship between climate change/global warming and
obesity is shown in [Fig. 7].
Fig. 7 The bidirectional relationship between climate change/global
warming and obesity.
Climate change will likely disrupt food availability, reduce access to food, and
making utilization more difficult and the overall stability of each (availability,
access, utilization) [106].
Climate risks to food security are greatest for poor populations and in tropical
regions. The coupled model intercomparison project for use in climate modeling
experiments and assessment efforts developed representative concentration pathways
(RCP) with RCP 2.6 being a low emissions scenario with extensive mitigation and a
CO2 concentration of approx. 421 ppm by 2100. This would lead to a
global average temperature rise of approximately 1 °C by 2050 with no
further change by 2100, and a global average sea level increase of approx.
0.17–0.32 m by 2050 and 0.26–0.55 m by 2100. The RCP
8.5 represents a high emissions scenario, where emissions continue to increase
rapidly, producing a CO2 concentration of 936 ppm by 2100, resulting in a
global average temperature rise of approximately 2 °C by 2050 and 4
°C by 2100. Global average sea level rise would be approx.
0.22–0.38 m by 2050 and 0.45–0.82 m by 2100.
Socioeconomic models, which include climate change generally show an increase in
food prices. Utilization rates are affected by food waste that occurs as a result of
climate sensitive activities during food storage, processing, packaging, and trade.
Food waste in the United States seems to account for 1 pound of food per day and to
generate 8% of global greenhouse gas emissions [107]. Diets lower in meat such as a
Mediterranean diet, have been estimated to reduce greenhouse gas emissions by
72%, land use by 58%, and energy consumption by 52% [108]
[109]
[110]. In the end, energy
expenditure including caloric intake remain a key component of weight maintenance
regardless of diet type [111] . Successful
long-term weight loss is difficult to achieve and a workshop at the National
Institute of Diabetes and Digestive and Kidney Diseases was held to discuss the
physiology of the weight-reduced state [112] .
The accumulation of data on key biological factors combined with behavioral,
psychosocial, and environmental factors can help designing and delivering effective
and tailored obesity treatments [113]. The
overall placebo-subtracted weight reduction for at least 12 months can range from
2.9 to 6.8% for the anti-obesity drugs phentermine/topiramate,
liraglutide, naltrexone/bupropion, and orlistat [114]. In obesity prevention, it is also
important to be aware of weight gain and body fat redistribution as common side
effects of many widely used medications such as antipsychotics [115].
In summary, there is a bidirectional relationship between climate
change/global warming and adiposity. Strategies that improve the health of
each individual on the planet and “save the planet” will meet
challenges in various parts of the world simply by political will, economic
considerations, cultural differences, infrastructure, and many other factors. In the
end, each individual has to try to make her/his own best effort and
contribution to live a healthier life.
