Temperatures around conception affect metabolic health in adulthood

Epigenetic adaptations around conception can help organisms adjust to their future environment. Pre-conception cold exposure is thought to increase active brown fat mass, and as brown fat metabolizes stored energy to generate heat, this helps adjust to life in cold environments. We examine the implications of this process for human metabolic health. We use data on 430,000 individuals born between 1934 and 1971 from the UK Biobank, and match these to historical temperature data. To isolate causal impacts of temperature, we utilize day-specific temperature deviations during the calculated pre-conception period relative to the long-term mean temperature for the same location and day of year. This approach leverages a quasi-random variation in temperature. We find that individuals conceived when temperatures were lower than usual have lower body mass indices (BMI), smaller waist circumferences, and lower levels of triglycerides and total cholesterol in adulthood, while there was no evidence for an effect on glycated hemoglobin (HbA1c). These findings have implications for potential health effects of climate change, and more strongly, for effects of improved indoor insulation.