# Temperatures around conception affect metabolic health in adulthood

## TL;DR

Being conceived during colder periods is linked to better metabolic health in adulthood, possibly due to epigenetic changes affecting fat activity.

## Contribution

The study shows that pre-conception temperature exposure has lasting effects on adult metabolic health through potential epigenetic mechanisms.

## Key findings

- Colder pre-conception temperatures correlate with lower BMI, waist circumference, and blood lipid levels in adulthood.
- A 2°C lower temperature at conception is associated with a 126g lower body weight in average adults.
- Effects on glycated hemoglobin were less pronounced compared to other metabolic markers.

## Abstract

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 437,504 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. Associations between pre-conception temperature exposure and adult metabolic health were estimated using regression models adjusted for relevant covariates.

Individuals conceived when temperatures were lower than usual have lower body mass indices, smaller waist circumferences, and lower levels of triglycerides and total cholesterol in adulthood, while the effect on glycated hemoglobin appeared to be less strong.

Our study indicates that pre-conception environmental conditions can influence human metabolic health, potentially through epigenetic mechanisms linked to brown fat activity. These findings have implications for potential health effects of climate change, and, more strongly, of improved indoor insulation.

We combined UK Biobank data from over 430,000 people with historical weather records, examining whether unusually cold or warm conditions before conception have lasting health effects. Previous research suggests that when fathers experience cold conditions before conception, their offspring may have more active brown fat, a type of fat that produces heat.

Our study shows that the temperature around the time a person is conceived influences their metabolic health later in life. People conceived during colder-than-usual periods tend to have lower body weight, smaller waists, and healthier levels of blood fats (triglycerides and cholesterol) as adults. For example, in an average adult, a 2 °C lower temperature at conception is associated with a 126 g lower body weight.

As global temperatures rise and better housing insulation keeps homes warmer during winter, long-term consequences for metabolic health can be expected.

Münz et al. link historical temperature data to over 437,000 UK Biobank participants to test how pre-conception cold exposure affects later metabolic health. Individuals conceived during colder-than-usual periods show lower adult BMI, waist circumference, and blood lipid levels, suggesting lasting epigenetic effects.