Research

Hormonal

Brown adipose tissue (BAT) activity in adult humans exhibits strong seasonal variation, with prevalence and intensity significantly higher in winter compared to summer, and this variation is more closely associated with photoperiod (night length) than ambient temperature.

Your body's fat-burning tissue (BAT) naturally fluctuates with the seasons, peaking in winter. This is driven more by day length than just cold exposure. Do not expect your metabolic rate to be identical year-round; however, this variation does not negate the importance of consistent healthy habits. If you are using cold exposure or other BAT-stimulating strategies, expect them to be more effective in colder months or shorter days.

GoodSupportsHIGH confidence
The month-to-month circannual variation is even more striking because it is inversely correlated with average monthly temperatures and positively related to night length... The difference in the monthly number of patients in which BAT activity observed was therefore positively correlated with night length (r2 = 0.876... P < 0.00001... and negatively correlated with ambient temperature (r2 = 0.696... P < 0.001).
Iain Au‐Yong et al. · Diabetes · 2009

Why this rating

Large retrospective observational study (n=3,614) with strong statistical correlation, but lacks mechanistic proof of causality for photoperiod vs temperature.

Source

Brown Adipose Tissue and Seasonal Variation in Humans

Iain Au‐Yong et al. · Diabetes · 2009

DOI 10.2337/db09-0833

cohort · n=3614Cited 272×
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DOI resolved against Crossref · corpus check 2026-06-10

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