Lack of sunshine and the vitamin it makes in our skin is probably the most serious single cause of disease in the UK today.

Vitamin D deficiency is well known as the classic cause of rickets and serious bone diseases, but in the last 10 years it has also been identified as a major risk factor for diabetes, heart disease, arthritis, infections, some cancers and other ills.

The cost of all this disease to the UK has been put at an astounding £27bn annually, which compares with only £5bn for the cost of disease caused by smoking.

Small amounts of vitamin D can be obtained from food but you can't obtain more than about 10 per cent of the optimal amount this way unless you eat oily fish – skin and all – three times a day.

We depend on the sun for our vitamin D. Since our weather is so unreliable, British people suffer more than almost any other from vitamin D deficiency.

Many years of bad advice has also been a factor.

The British Isles are located far north so the winter sun is not strong enough to make any vitamin D. The prevailing westerly wind bringing cloud in from the Atlantic is also against us. The Scots are worst off because there is nothing to the west to protect them. Their vitamin D levels are lower and they have the highest incidence of multiple sclerosis in the world.

Scientists studying MS now believe that it may be prevented if women take vitamin D in pregnancy and children take regular supplements. Another devastating disease, diabetes type 1 – affecting mostly children who must inject themselves with insulin – could be prevented by the same vitamin D supplements.

Indeed it is possible that these two diseases could now be eradicated if Government had the will.

However a recommendation that pregnant women take vitamin D has been ignored over many years by obstetricians.

Standard advice is that babies are not given vitamin D until they are six months old. Nobody any longer remembers the reason for this, which is implemented nowhere else.

Everybody thinks that breast milk is a complete food – and so it might be if mothers sunbathed as often as they can. As it is, breast milk in the UK is deficient in vitamin D while artificial milk is supplemented.

This need not be a problem if mothers give vitamin D drops to their babies. Melanoma, the worst form of skin cancer, has dramatically increased during some 20 years of advice to avoid the sun and use suncream. This is quite possibly because the advice has been wrong. Suncream blocks the action of UVB (shortwave ultraviolet radiation from the sun) – so blocking synthesis of vitamin D with loss of protection against cancer – while UVA (longwave radiation), which seems to carry the main risk of melanoma, is not blocked by many creams.

We could do much, much more. The Irish Republic has already fortified semi-skimmed milk with vitamin D, Finland has fortified milk and Israel is making milk fortification mandatory. Jordan is bringing in fortification of bread.

The UK the Food Standards Agency has hummed and hawed. The United States has had fortification for 80 years. What are the English and Scots waiting for?

The one simple action open to us all is to sunbathe, carefully without burning. The sun is natural, free, and safe if you are sensible. It's also good to take a vitamin D supplement of at least 1000 to 2000 IUs [international units of measurement] per day.

The author is a health writer and vitamin D campaigner