Why a hot summer can be a real bummer... for men

WITH temperatures forecast to reach up to 25C in parts of the country this week, many of us may find ourselves gunning for an ice cream or a few chilled pints in a beer garden.

But scientists claim it may not just be our desire to cool off that leads us to reach for these treats in the sunshine.

A new study has found that exposure to sunlight stimulates the release of a hunger hormone from the skin – but the effects are only prevalent in men.

Researchers from Tel Aviv University in Israel claim that males are more likely to gain weight in the summer due to this hormone.

However, in women, the sex hormone oestrogen interferes with the release of this hormone, so there’s no change in appetite.

The study, published today in Nature Metabolism, looked at the results of a survey of 3,000 Israeli participants who recorded their diet between 1999 and 2001.

Carmit Levy and her team saw that, on average, men increased their intake of calories in the summer months. However, women did not show a similar summer peak.

The research was supported by a study of mice that were exposed to daily ultraviolet (UVB) radiation for ten weeks. The researchers observed a ‘significant increase in food intake’ in the male mice but not the females.

It was found that the UVB radiation stimulated the release of the hunger hormone ghrelin from the fat cells in the skin tissue of male mice. Upon reaching the hypothalamus, the ghrelin increased appetite in these male mice, promoting food intake and weight gain. Female mice with low oestrogen also exhibited higher food intake.

The researchers believe their results identify skin fat as a possible regulator of feeding behaviour, adding a new type of fat tissue to the energy balance equation.

However, Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, believes that other factors may have influenced these results.

He said: ‘The results in mice and cell cultures and the other human studies do at least make it plausible that solar radiation and sex differences could be involved in causing the patterns, but it’s also plausible that men and women behave differently in relation to sunny weather for social reasons.’