Health: The healing power of sunlight

But it has recently been revealed that the national condition may have less to do with genetics or a generally miserable outlook on life, and more to do with the weather. Because, while we never tire of complaining about our dark, dreich winters – those long months in which we never seem to see daylight, let alone sunlight – it turns out they really can contribute to depression.

It's all to do with vitamin D, which is created by the body when sunlight hits the skin. And since vitamin D helps release melatonin in the brain – which in turn makes us feel happy – when we don't see the sun for long periods of time, the result is all-out misery. Is it any wonder our suicide rate is the highest in the UK?

Jane Watt, a mother-of-three from Edinburgh, says: "I've been feeling really low for weeks now and I couldn't put my finger on what it was all about. Life is fine, the children are healthy, I've been eating well.

"Then it hit me. I didn't manage to have a holiday abroad this year. And because we had such a rubbish summer at home, I feel I've hardly seen the sun all year. I've heard a lack of vitamin D can cause depression, and that makes complete sense to me."

But it's not just our mood that can be improved with a sunlight boost. Vitamin D deficiency has been linked to an increased risk of heart disease, stroke, cancer and multiple sclerosis. It could even make us fat. You'd think this dramatic news would help solve both our famed grumpiness and our appalling health record in one fell swoop. But since the nation's GPs are unlikely to start prescribing a fortnight in Magaluf for every Scot claiming to be down in the dumps, how can we address the problem?

Last year, a team from Dundee University proved it could be as simple as popping some vitamin pills over the winter months. When it boosted the intake of a group of volunteers, their heart function was found to improve noticeably. Professor Allan Struthers, from the university's medical school, said: "It was a small group but the findings fit very nicely with what we already know – that heart disease is more common in northern latitudes, deaths from heart disease are more prevalent in winter than summer, and in Scotland we don't make any vitamin D in the wintertime."

He now believes the development of a single dose of vitamin D, to be taken in the autumn, could help protect those at risk of heart attacks or strokes during the darkest months. "One of the good things about vitamin D is that it is a fairly non-toxic substance and having one pill every two or three months would be much easier for people than having to take a pill every day."

It's not just our hearts that could benefit. In July, a study at Aberdeen University discovered a possible link between vitamin D and obesity. Dr Helen MacDonald, from the university's department of medicine and therapeutics, said of her findings: "Obese people had less vitamin D and the link between obesity and vitamin D deficiency was statistically significant. It could be because people are not getting enough sunlight or that they do not go out much. There's also the possibility that their vitamin D is locked into fat stores."

And, at Oxford University, scientists found that babies born in the springtime were more likely to develop multiple sclerosis than those born in the autumn. This was thought to be because mothers who were pregnant during the summer were exposed to greater levels of sunlight and so had higher levels of vitamin D in their bodies.

Furthermore, this link was most noticeable in the Scottish results. The university's Professor George Ebers said: "Scots have the highest birth-month effect; and the further north you go, the stronger the link becomes."

Around 10,500 Scots have MS, and the study, published in the British Medical Journal, established that the risk of contracting the disease increased by 13 per cent for babies born in May, but dropped by 19 per cent for those born in November.

If you needed more convincing, in September, scientist and writer Dr Oliver Gillie called for GPs to be able to prescribe massive doses of the vitamin to patients – up to 50 times the current daily recommendation – in a bid to improve the nation's health. In his report, Scotland's Health Deficit: an Explanation and a Plan, he also proposed that foods such as bread, orange juice and milk be fortified with the vitamin, and urged the government to take "urgent action" on the issue.

He said: "Scotland has an extreme climate characterised by very little sunshine – it gets as little sunshine as some places in the Arctic Circle. Its people have low levels of vitamin D. Scots also have high levels of chronic illness – among the highest in the world. But vitamin D has received little or no attention from policy-makers in Scotland."

However, some health experts have warned that supplements are not the answer. For although the body is able to regulate the amount of vitamin D it creates from exposure to sunlight, tablets can override that natural metabolism, and an overdose could result in kidney stones, since the vitamin helps to control the amount of calcium in the body.

Nor should this be seen as a green light to lie in the sun at every opportunity. Five minutes' exposure on a hot day is all it takes to maintain a healthy level of vitamin D in the body; any more and you could be increasing your risk of skin cancer.

The A-z to vitamin D

• The skin produces vitamin D in response to exposure to the ultraviolet radiation contained in natural sunlight.

• The rays can't pass through glass so you don't get the benefits sitting in your house or your car.

• Although vitamin D is found in eggs, milk and oily fish, it is almost impossible to get enough through your diet alone.

• Those with fair skin generate much more vitamin D than those with darker skins, which is why prostate cancer is so much more widespread among black men.

• Vitamin D is vital for the body to absorb calcium.

• Using a sunscreen blocks the body's ability to generate vitamin D by up to 95%.

• Your body cannot make too much vitamin D; it self-regulates and will only create what it needs. But it is possible to overdose on supplements.

• Press firmly on your sternum – if it hurts, it is possible you are suffering from chronic vitamin D deficiency.

• Vitamin D deficiency has also been linked to adrenal insufficiency; Alzheimer's disease; various allergies; autoimmune disorders, including multiple sclerosis and rheumatoid arthritis; cancers of the colon, breast, skin and prostate; depression; seasonal affective disorder (Sad); diabetes types 1 and 2; gluten intolerance; lectin intolerance; heart disease; hypertension; infertility; learning and behavioural disorders; misaligned teeth and cavities; obesity; osteoporosis; rickets (right); Parkinson's; PMS; and psoriasis.

This article was first published in Scotland on Sunday, March 14, 2010