Dr Damien Downing is a former York GP who now specialises in nutrition.

Q At this time of year, around when the clocks go back, I start to feel really tired and depressed, and I find myself bingeing on stodgy foods and then I put on pounds. I usually get better in the spring, but until then my life is miserable.

AThis sounds just like SAD, Seasonal Affective Disorder. Sufferers usually feel a change for the worse when the clocks change, because the amount of sunlight you see each day drops suddenly, and this is what triggers the syndrome.

You describe exactly the symptoms most sufferers experience, and researchers suspect that as many as 20 per cent of us suffer from some degree of SAD. The treatment is light; assuming you can't relocate to the Med, you could buy a bright light and use it daily - Boots sells the Philips Brightlight for less than £200 and you can get VAT off as a medical device - or you might get the same benefit from taking a walk for an hour every morning.

One recent study found that St John's Wort was also helpful (until we know more, I don't advise you using both this herb and light therapy).

Light also appears to help in ordinary, non-seasonal depression, showing results as good as antidepressants.

You may have guessed that this is something of a fascination for me - I wrote a book about the benefits of sunlight back in 1988, Daylight Robbery, which I hope to update and reissue next year.

I am convinced that sunlight is an essential nutrient, just like vitamins, that helps to prevent infections, depression, osteoporosis, cancer, MS, ME and other complaints.

And yes, I did say cancer; there's no room to go into all that here, but although light may, perhaps, contribute to melanoma (a skin cancer), it seems to help prevent internal cancers, which are a lot more common and more lethal.

Q In winter I seem to get every bug going - colds, flu, the lot. What can I do to prevent this?

A Well, see the previous question for a start! Light is one factor that influences our immune systems and general health. But there are several nutrients that we all need, and don't always get enough of, particularly in winter.

Zinc and Vitamin C are probably the most important and it is worth taking supplements of these two; capsules of Zinc (20 to 40mgs per day, depending on your weight) and C (ascorbic acid; 2000 to 4000mgs) will help your body to fight off infections.

Also important are the essential fatty acids or EFAs, which your body uses to make the walls of every single cell. Take a supplement such as Efamarine (in most health shops) or similar. In your diet, EFAs are in vegetables, salads and fruit, which provide lots of the vitamins and minerals you need as well, so make sure you get at least the recommended five portions per day, the fresher the better.

Eat oily (not white) fish too, at least twice a week, and go easy on the animal fats and sugary foods, which can crowd out these essential nutrients.

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