Jennifer Viegas
Discovery News


Tuesday, 13 June 2006

Lean in summer, curvy in spring
Hormonal changes linked to the seasons may change the shape of your body during the year (Image: iStockphoto)
Seasonal changes cause fat to shift locations in our body, altering the shape of our figures at certain times of the year, according to a new study.

Varying testosterone levels drive the shape changes, the study, which has been accepted for publication in the upcoming issue of Psychoneuroendocrinology suggests.

The hormone, often associated with brawn and aggressiveness, fluctuates over the seasons in both men and women.

The most evident changes occur around the waist and hip region, the study says. When testosterone levels rise, women became less curvy and fat shifts toward the waist.

Other research has determined that the opposite happens in men, who retain more fat in the abdominal region when testosterone levels fall.

The scientists examined seasonal testosterone fluctuations in the saliva of 220 women and 127 men. They also measured the waists and hips of the female study participants over the seasons.

Women more curvaceous in winter
"We found that women's and men's testosterone is highest in autumn," says Sari van Anders, a PhD student at Canada's Simon Fraser University who led the research.

"As well, women's waist-to-hip ratio (how big the waist is relative to the hips) is highest during autumn, and central measures of fat deposition, like abdominal fat, were also somewhat higher in autumn (for women)."

Women also had high testosterone levels in summer. Men showed lowest testosterone levels in spring.

Van Anders, a doctoral candidate in behavioural neuroendocrinology, says "This suggests that patterns of fat deposition, but not overall fat, are slightly different depending on the season, with more fat being deposited in the central waist region in autumn (in women)".

The study suggests women look more curvaceous in winter and spring.

Men, Van Anders says, look manlier during spring when waist and hip size becomes more uniform and less feminine.

"While we didn't test this, a large body of previous research has found that men find lower waist-to-hip ratios in women more attractive in Western nations," van Anders says.

"As well, a large body of research finds that lower waist-to-hip ratios are associated with better fertility parameters and health parameters. This suggests that women should be perceived as slightly less attractive in autumn."

The researchers don't know whether the changes are apparent on a conscious or subconscious level, since they occur gradually over time and do not dramatically alter appearance.

It's all about reproduction

Randy Nelson, a professor of psychology and neuroscience at Ohio State University, and one of the world's leading experts on how the seasons affect humans and animals, says the study "is a novel and important finding".

"There have been previous demonstrations of seasonal changes in hormones, including testosterone, in humans, as well as seasonal influences on the timing of conception," he says.

"About 6 years ago, a graduate student of mine even showed seasonal changes in cognitive performance among people!"

The scientists are not sure why these fluctuations in body shape exist.

Van Anders says the changes might be byproducts of testosterone changing seasonally for reasons unrelated to waist-to-hip ratio, such as health, immune function, fertility and behaviour.

News in Science - Seasons change your body shape - 13/06/2006

thought this was semi interesting