A recent study published in Nature Metabolism has revealed that the season during which you were conceived could have a significant impact on your body’s calorie-burning ability, potentially influencing your risk for obesity and metabolic diseases later in life. Researchers from Japan examined how exposure to colder temperatures before conception can boost brown fat activity and lifelong energy expenditure in humans. Their findings suggest that environmental cues before conception, specifically temperature fluctuations, may play a critical role in shaping our metabolism.
Background
Why do some people seem to stay slim, even when they consume more calories? Surprisingly, the answer may lie in the weather conditions before they were even conceived. Brown adipose tissue (BAT), also known as brown fat, helps our bodies burn calories by generating heat, particularly in cold conditions. While brown fat is more active in infants, its activity tends to decline with age. However, in some individuals, this process may not follow the typical trajectory.
In mice, cold environments before pregnancy can “pre-program” fat-burning traits in offspring, but can this phenomenon occur in humans as well? With rising obesity rates and the effects of climate change, understanding how early environmental factors influence metabolism could provide crucial insights into preventive health strategies.
About the Study
The study involved 748 healthy adults from five Japanese cohorts, with participants selected based on a thorough screening process. Researchers used several advanced methods, including fluorodeoxyglucose-positron emission tomography (FDG-PET/CT), near-infrared time-resolved spectroscopy (NIR-TRS), and doubly labeled water (DLW) to measure brown fat activity and total daily energy expenditure (TEE). The study also assessed cold-induced thermogenesis (CIT) and diet-induced thermogenesis (DIT) to understand how much energy participants burned when exposed to mild cold or after eating.
Participants were categorized into two groups based on their estimated fertilization seasons: “cold” (October 17–April 15) and “warm” (April 16–October 16). This classification was based on Japan’s seasonal temperature patterns. Researchers then analyzed the data to determine how the timing of conception affected brown fat activity, energy expenditure, and body mass index (BMI).
Study Results
Increased Brown Fat Activity in Cold-Conceived Individuals
The study revealed a significant trend: people conceived during colder months showed more active brown fat in adulthood. In Cohort 1, 78% of individuals conceived during the cold season had detectable brown fat activity, compared to only 66% of those conceived during the warm season. This effect was tied to the time of conception rather than birth season.
Using NIR-TRS in Cohort 2, researchers found that individuals conceived in colder months had significantly higher brown fat density, particularly in the neck and shoulder areas, where brown fat is most commonly located. This pattern held true for both men and women, suggesting that the effect of seasonal conception could be generalized across genders.
Increased Energy Expenditure in Cold-Conceived Individuals
Further analysis in Cohort 3 showed that those conceived during the cold season burned more energy after exposure to cold air (CIT). They burned 1.5 times more calories than those conceived during warmer months, with the greatest effects observed in winter. This suggests that cold-induced thermogenesis plays a crucial role in energy expenditure and is linked to the timing of conception.
In Cohort 4, researchers assessed diet-induced thermogenesis (DIT) and found similar results: individuals from the cold-fertilization group burned more calories after meals. Cohort 5, using the DLW method, confirmed that cold-conceived individuals had higher TEE in daily life, even when adjusting for physical activity levels and body composition.
Brown Fat Activity in Children
Cohort 5 also included toddlers aged 3–6, showing that cold-conceived children exhibited higher brown fat activity even before puberty, suggesting that the benefits of cold-season conception could be seen from a young age.
Lower BMI and Health Benefits in Cold-Conceived Adults
Participants from Cohort 2, which included adults of various ages, demonstrated that those conceived during colder months had lower BMI, less visceral fat, and smaller waistlines. These individuals’ higher brown fat activity was associated with these positive health outcomes. In younger adults (Cohort 1), BMI differences were minimal, likely because they had not yet experienced age-related fat gain.
What Caused This Effect?
Weather data analysis revealed that lower outdoor temperatures and greater day-night temperature fluctuations during the months prior to conception were the strongest predictors of adult brown fat activity. This finding suggests that the critical window for programming metabolism may occur before fertilization, rather than during pregnancy itself.
The researchers hypothesize that epigenetic changes in sperm caused by paternal cold exposure may be responsible for this phenomenon, a mechanism observed in mice but not yet confirmed in humans.
Conclusion
This study suggests that being conceived during colder months can boost brown fat activity and increase long-term energy expenditure, potentially lowering the risk of obesity in adulthood. It introduces the novel concept of “Pre-fertilization Origins of Health and Disease” (PfOHaD), highlighting how environmental factors before conception can shape our metabolic health across generations. As global temperatures rise and obesity rates continue to climb, this research offers valuable insights into how early environmental exposures might influence our health trajectory, urging the need for further studies in diverse global populations. Understanding this connection could pave the way for new preventive strategies against metabolic diseases.
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