Abstract
Blood urea nitrogen (BUN) is a key metric when evaluating the renal function of a
given patient. Individuals with chronic kidney disease also often present with
abnormal thyroid functionality. The specific association between BUN and thyroid
function, however, is not well understood. This study was thus developed to
explore how BUN levels within the normal range are related to thyroid activity
among adults in the USA. The National Health and Nutrition Examination Survey
(NHANES) dataset was leveraged for these analyses. Linear regression and
smoothed curve fitting approaches were employed to examine the association
between BUN levels and measures of thyroid function, with appropriate weighted
and subgroup analyses. The 2007–2012 NHANEs cycles included 6231 eligible adults
with BUN levels from 2.5–8.0 mmol/l. Under adjusted models, a higher BUN level
was associated with reductions in FT3 (β=–0.01; p=0.047), TT3 (β=–1.08;
p=0.003), and TT4 (β=–0.10; p=0.003) levels. In subgroup analyses, BUN levels
were respectively found to be negatively correlated with FT3 and TT4 levels in
subjects who were inactive and active. These findings are consistent with
reduced FT3, TT4, and TT4 levels being correlated with higher BUN levels within
the normal range among American adults. In non-physically active subjects, FT3
levels were more closely related to increasing BUN levels, whereas TT4 levels
were more closely related to BUN levels among physically active subjects.
However, additional research will be vital to clarify the mechanisms that
underlie these results.
Keywords thyroid function - blood urea nitrogen - NHANES - kidney function
