Sleeping with too much light in the room increases the risk of obesity, diabetes, and depression

A poor set of curtains may not just mean you wake up too early - they could also make you fat.  A study has found that sleeping with too much light in the room increases the risk of obesity in women.Greater exposure to light at night raised both Body Mass Index (BMI) and waist size in more than 113,000 women taking part in the British study.

The Breakthrough Generations Study followed the women for 40 years in

an attempt to identify root causes of breast cancer. Obesity is a known

risk factor for the disease.
Professor Anthony Swerdlow, from The Institute of Cancer Research in

London, said: 'Metabolism is affected by cyclical rhythms within the

body that relate to sleeping, waking and light exposure.

'The associations we saw in our study between light exposure at night

and obesity are very intriguing.
'We cannot yet tell at this stage what the reason for the associations

is, but the results open up an interesting direction for research.'
Co-author Dr Emily McFadden, a visiting researcher at the the

institute, said: 'Because all the information was collected at the same

time, we cannot tell the sequence of events.

'But the associations we found are consistent with previous research

examining light exposure and metabolism, and further investigation is

needed.'
The study was funded by the charity Breakthrough Breast Cancer, whose

senior research officer Dr Matthew Lam said: 'These findings add weight

to previous results from animal studies that looked into how light

exposure, circadian rhythms and metabolism could all be connected in

some way.

'It's too early to suggest that sleeping in the dark will help prevent

obesity, a known risk factor for breast cancer, but the association is

certainly interesting.'
The findings are reported in the American Journal Of Epidemiology.
Previous research has drawn similar conclusions. A team at Ohio State

University examined how nocturnal light affects weight, body fat and

glucose intolerance (the underlying cause of late-onset diabetes) in

mice.
They found that persistent exposure to even a little night-time light

caused increases in all three.
Another report from the American Medical Association found the

disruptive effect of nighttime lighting on our bodies' circadian

rhythms may contribute to 'obesity, diabetes, depression and mood

disorders, and reproductive problems'