Exposure to bright light boosts the sex drive of men over 40, a study has found.

It showed their testosterone levels rose and they enjoyed greater sexual satisfaction after regularly standing in front of a light box typically used to treat seasonal affective disorder.

The study was inspired by previous research showing male sexual desire fluctuates with the seasons, decreasing in darker winter months.

It focused on men over 40 because one in four in this age group reports problems with sexual desire.

The Italian researchers considered 38 men with one of two conditions characterised by a lack of interest in sex – hypoactive sexual desire disorder or sexual arousal disorder.

A new study has found that exposure to bright light boosts the sex drive of men over 40

Their testosterone levels and interest in sex were established before they were divided into two groups.

One received regular treatment with a box that emitted 10,000 lux of light – the equivalent of bright daylight – from a distance of one metre.

The other group was exposed 100 lux, the amount of light on a very dark overcast day. Both groups used the light box for around 30 minutes every day between 7am and 8am, for two weeks.

The men were then retested and the researchers found those exposed to bright light reported sexual satisfaction levels three times higher than before the treatment, while there was no significant change in the other group.

Professor Andrea Fagiolini, who conducted the study with colleagues at the University of Siena, said: 'Before treatment, both groups averaged a sexual satisfaction score of around two out of ten, but after treatment the group exposed to the bright light was scoring around 6.3 – a more than three-fold increase.

'In contrast, the control group only showed an average score of around 2.7 after treatment.'

The researchers also found testosterone levels increased in men who had bright light treatment, from around 2.1 nanograms per millilitre to 3.6ng/ml after two weeks.

The group exposed to low light showed no significant change – their testosterone level was around 2.3ng/ml at both the beginning and the end of the experiment.

Professor Fagiolini told the European College of Neuropsychopharmacology's annual congress in Vienna: 'The increased levels of testosterone explain the greater sexual satisfaction.'

He added: 'In the northern hemisphere, the body's testosterone production naturally declines from November through April, then rises through the spring and summer with a peak in October.

The study was inspired by previous research showing male sexual desire fluctuates with the seasons, decreasing in darker winter months

'You see the effect of this in reproductive rates, with the month of June showing the highest rate of conception. The use of the light box really mimics what nature does.'

He said light therapy might work by inhibiting the pineal gland in the brain to increase testosterone production, but 'there are probably other hormonal effects'.

He added it could not yet be recommended for clinical use, but if it worked in a larger study, 'light therapy may offer a way forward'.