Vitamin D’s importance in maintaining strong, healthy bones through its interaction with the essential mineral, calcium, is well known. But the vitamin is also vital for the health of the nervous and immune systems, in regulating insulin levels and blood pressure, and even as a possible protector against certain common cancers.

The best known and most serious disease associated with vitamin D deficiency is rickets, which arises when the deficiency causes blood calcium levels to fall too low, and the body to respond by stripping the bones of calcium leading to loss of bone density and malformation.

Interestingly, studies have shown that the geographical pattern of the incidence of rickets is very similar to those for both breast and colon cancer, suggesting a possible (though not fully understood) link between vitamin D deficiency and these diseases. One 5 year study which grouped 120,000 people by levels of vitamin D intake reported that men in the highest intake group had a 29% lower incidence of colon cancer than those in the lowest intake group and similar results have been observed in breast cancer research. Relatively high blood levels of active form vitamin D have also been associated with a lower risk of pre-cancerous growths (polyps) in the colon whereas lower levels of vitamin in the blood have been associated with an increased risk of prostate cancer.

Vitamin D is known to be essential for a healthy immune system and has been shown to be particularly important in helping prevent auto-immune diseases – those in which the body’s immune system attacks and destroys its own cells, wrongly having identified them as invaders. Type 1 (insulin dependent) diabetes, rheumatoid arthritis and multiple sclerosis are examples of serious diseases which fall into this category and a number of research studies suggest that a generous intake of vitamin D may be a significant mitigating factor.

Blood levels of vitamin D have also been shown to be inversely correlated with blood pressure, and some research suggests that high dose supplements of vitamin D of (1,600 IU per day) may help this, although orthodox medicine, as ever, is cautious about definitively acknowledging any direct causal link.

The traditional view was that adequate supplies of vitamin D can be synthesised in the skin upon its exposure to sunlight. But the problem is that a large proportion of the population in the affluent world lives in latitudes which provide very limited sunlight for six months of the year. People commonly work indoors and tend to use high factor sunblocks on the rare occasions on which they might expose significant areas of skin to the sun.

It is a cruel irony that this concern about skin cancer may lead to the ill-health associated with vitamin D deficiency and may even increase the risk of other cancers. But in these circumstances the usual assumptions about vitamin D production in the body appear questionable at best, if not downright complacent. And the situation is even worse for the elderly, who may not only enjoy even less exposure to the sun than the young, but are less able to make use of that which they do obtain.

Moreover, there are relatively few good natural food sources of vitamin D, and the best source, oily fish such as sardines, mackerel and salmon is one which many people, and perhaps children in particular, often find unpalatable. The situation has improved somewhat with the fortification of milk, orange juice, bread and some cereal products, but it may still be difficult for individuals to ensure they obtain a sufficient intake of the vitamin, particularly because the amounts added to different foods and drinks are very variable.

Since the amount of vitamin D required from food will vary greatly depending on the amount of exposure to sunlight enjoyed by the individual, it has not been deemed possible to determine a Recommended Dietary Allowance (RDA) for vitamin D. But the Food and Nutrition Board has suggested 200 IU (5mcg) for infants, children, and adults up to 50, rising to 400 IU for the 50-70s, and 600 IU for the over 70s, as an “Adequate Intake” of the vitamin from food on the assumption that none is being obtained from sunlight.

Orthodox opinion, however, seems to regard these suggestions as too conservative. And even for those individuals fortunate enough to enjoy regular exposure to good quality sunlight, the intake of 400 IU (10 mcg) of vitamin D as part of a multi-vitamin and multi-mineral supplement is recommended. For the over 65s, those with less than optimal liver or digestive health, those living in less advantageous climates and those who spend the majority of their time in indoor occupations a supplementary dose of a further 400 IU, for a total of 800 IU is strongly advised.

For maximum effect, however, vitamin D supplementation should be always be combined with adequate dietary calcium – supplemented if necessary to achieve an intake of 1,000 – 1,200 mg per day of this essential mineral.