The 'healthy tan' may not be a complete myth. Sunshine is good for you - in moderation. Now winter's coming and the woolly jumpers are emerging, Hester Lacey asks: are you getting enough?
SUMMER'S GONE, holidays are a distant memory. The hazy days when the weather forecaster would solemnly intone the day's "burn time" seem like a dream. But now - even as you pull on your black woolly tights or dig out your cosy jumper - is the time to start thinking seriously about sunshine and how much you are getting (or not).

Seasonal Affective Disorder (SAD) has been recognised for about a decade as a disorder that affects a small percentage of the population, causing depression, forgetfulness and an increased desire to sleep during the winter months - almost like human hibernation. Sufferers are treated by spending several hours a day in front of light boxes that mimic natural daylight.

But according to Dr Damien Downing, diagnosed SAD sufferers are the tip of the iceberg. Dr Downing, a specialist in nutritional medicine and allergies, and the editor of the Journal of Nutritional and Environmental Medicine, believes that everyone could benefit from increased exposure to sunlight - particularly in winter months. He points to American experiments that have shown that light therapy does not only help sufferers of SAD, but also helps many patients with general depression. "The picture is getting more and more interest- ing," he says. "It seems that up to 60 per cent of the population may be helped."

Why is light so important? "There is a hormone called melatonin - the hormone of darkness - it's my vote for the molecule of the decade," explains Dr Downing. "It's not exactly a sedative, but more of a relaxant - it doesn't send you to sleep but it enables you to sleep. It is also the most potent anti-oxidant known to man and is involved in the regulation of the immune system. Melatonin is produced by the pineal gland, in the brain behind the forehead, in circumstances of darkness - it works best at night, the body is more receptive to it at night. Against that, you have to set increasing evidence that vitamin D is the hormone of light. It looks as though we need light during the day to trigger the secretion of vitamin D, but we also need the swing from bright light to darkness to produce melatonin."

This, it seems, is where winter gloom and artificial lighting in the workplace conspire against the pasty Brits. "The way we live, we often don't get bright light during the day, and we get partial light at night from street lighting and so on. The obvious first step is to get out into the light." Getting out in the middle of the day with sleeves rolled up is enough to get the beneficial effects of sunlight for around eight months of the year in this country, he says. So what about the remaining four? "You either go on expensive holidays to the Caribbean, or you install a light."

Dr Downing admits that research into the effects of light is still in the experimental stage. "It's controversial, and some aspects are difficult to prove - for example that melatonin stimulates the immune system, or that it may have a beneficial effect on hyperactivity - there are many threads to pull together." But he is not alone in thinking that sunlight has a beneficial effect. Dr Tim Bullock, consultant psychiatrist at St Mary's Hospital Medical School, has conducted research into SAD. "Research on the population in general shows that over half see their moods worsen in winter, and the cause may be that there is a direct relationship between sunlight and mood," he says.

"It seems quite likely that we have evolved to require a certain amount of sunlight - the desire to go out in it is natural. The only problem is that sunlight isn't what it used to be, because of the chemicals in the atmosphere that have taken away the filter that protected us for a million years."

Australian doctors have prescribed light therapy for panic attacks, after noticing that sufferers experience more attacks in winter. Ultra-violet light also encourages the production of endo- morphins, hormones that give a feeling of well-being.

But what about the well-documented down-side of the sun? Of the people who do visit their doctors with a dodgy mole, 40,000 are diagnosed with skin cancer every year. Around five per cent of cases prove fatal, and exposure to the sun has been identified as one of the causes of skin cancer. Apart from this, sun-worshippers can expect to end up with a prune-like complexion, even if they heed the multi-million pound advertising campaigns waged every summer by sun cream manufacturers.

The wary need not fear, says Dr Downing. Artificial lights used in therapy do not lead to tanning or skin damage. Anyway, he says, "burning is bad for the skin - not tanning. If you are regularly exposed to the sun, as well as a tan you get a solar callus - the top layers of the skin thicken up. This is not damage, but the body adapting - this protects you against the subsequent risk of burning. People who go to Ibiza and spend the day on the beach and peel are getting an overdose." Perhaps all the more reason to concentrate on the sun in the winter.