Obesity: A Connection to Climate?

Environmental factors around the time of birth may contribute to obesity later in life. Researchers in Great Britain and at Northwestern University believe that early exposure to cold, along with high birth weight, may make some individuals, especially males, susceptible to obesity in adulthood (Int J Obesity 2000;24:281).

Among 1165 men and 585 women in Hertfordshire, England born between 1920 and 1930, adult body mass index (BMI) was statistically related to the subject’s weight at birth. The study population included Caucasian men and women who had complete health records and who had lived in East or Northwest Hertfordshire since birth. Trends to increasing BMI or prevalence of obesity with increasing birth weight were statistically significant among men born in years following a cold winter, but not among men born after a mild winter. Although weights at 1 year of age did not show statistically significant seasonal trends, the relationship between birth weight and adult obesity was more pronounced in men and women born during the first 6 months of the year than those born during the last 6 months.

Birth environment

The findings suggested that environmental factors at work around the time of birth are associated with an increased prevalence of obesity in adulthood. This is not an entirely new concept: More than 150 years ago, a scientist proposed a general rule that body size among mammals increases from warmer to cooler climates (Am Anthropol 1953; 55: 311). And, nearly 50 years ago, Newman and Munro showed an inverse relation between weight for height and the average January temperature in the state of birth (Am J Phys Anthropol 1955; 13:1). The authors note that factors that are sensitive to both temperature and season, such as nutrition, may also be involved in the pattern of later obesity. However, they add that evidence from animal studies indicates that exposure to lower temperatures before and soon after birth promotes development of adiposity in the newborn (Am J Physiol 1998; 274:R398).