| In addition to its well known role in | | | | the problem is that a large proportion of the |
| maintaining healthy bones,vitamin D is also | | | | population in the affluent world lives in |
| vital for the health of the nervous and | | | | latitudes which provide very limited sunlight |
| immune systems and may help protect against | | | | for six months of the year. People commonly |
| cancer. | | | | work indoors and tend to use high factor |
| | | | sunblocks on the rare occasions on which they |
| Vitamin D's importance in maintaining strong, | | | | might expose significant areas of skin to the |
| healthy bones through its interaction with | | | | sun. |
| the essential mineral, calcium, is well | | | | |
| known. But the vitamin is also vital for the | | | | It is a cruel irony that this concern about |
| health of the nervous and immune systems, in | | | | skin cancer may lead to the ill-health |
| regulating insulin levels and blood pressure, | | | | associated with vitamin D deficiency and may |
| and even as a possible protector against | | | | even increase the risk of other cancers. But |
| certain common cancers. | | | | in these circumstances the usual assumptions |
| | | | about vitamin D production in the body appear |
| The best known and most serious disease | | | | questionable at best, if not downright |
| associated with vitamin D deficiency is | | | | complacent. And the situation is even worse |
| rickets, which arises when the deficiency | | | | for the elderly, who may not only enjoy even |
| causes blood calcium levels to fall too low, | | | | less exposure to the sun than the young, but |
| and the body to respond by stripping the | | | | are less able to make use of that which they |
| bones of calcium leading to loss of bone | | | | do obtain. |
| density and malformation. | | | | |
| | | | Moreover, there are relatively few good |
| Interestingly, studies have shown that the | | | | natural food sources of vitamin D, and the |
| geographical pattern of the incidence of | | | | best source, oily fish such as sardines, |
| rickets is very similar to those for both | | | | mackerel and salmon is one which many people, |
| breast and colon cancer, suggesting a | | | | and perhaps children in particular, often |
| possible (though not fully understood) link | | | | find unpalatable. The situation has improved |
| between vitamin D deficiency and these | | | | somewhat with the fortification of milk, |
| diseases. One 5 year study which grouped | | | | orange juice, bread and some cereal products, |
| 120,000 people by levels of vitamin D intake | | | | but it may still be difficult for individuals |
| reported that men in the highest intake group | | | | to ensure they obtain a sufficient intake of |
| had a 29% lower incidence of colon cancer | | | | the vitamin, particularly because the amounts |
| than those in the lowest intake group and | | | | added to different foods and drinks are very |
| similar results have been observed in breast | | | | variable. |
| cancer research. Relatively high blood | | | | |
| levels of active form vitamin D have also | | | | Since the amount of vitamin D required from |
| been associated with a lower risk of | | | | food will vary greatly depending on the |
| pre-cancerous growths (polyps) in the colon | | | | amount of exposure to sunlight enjoyed by the |
| whereas lower levels of vitamin in the blood | | | | individual, it has not been deemed possible |
| have been associated with an increased risk | | | | to determine a Recommended Dietary Allowance |
| of prostate cancer. | | | | (RDA) for vitamin D. But the Food and |
| | | | Nutrition Board has suggested 200 IU (5mcg) |
| Vitamin D is known to be essential for a | | | | for infants, children, and adults up to 50, |
| healthy immune system and has been shown to | | | | rising to 400 IU for the 50-70s, and 600 IU |
| be particularly important in helping prevent | | | | for the over 70s, as an "Adequate Intake" of |
| auto-immune diseases - those in which the | | | | the vitamin from food on the assumption that |
| body's immune system attacks and destroys its | | | | none is being obtained from sunlight. |
| own cells, wrongly having identified them as | | | | |
| invaders. Type 1 (insulin dependent) | | | | Orthodox opinion, however, seems to regard |
| diabetes, rheumatoid arthritis and multiple | | | | these suggestions as too conservative. And |
| sclerosis are examples of serious diseases | | | | even for those individuals fortunate enough |
| which fall into this category and a number of | | | | to enjoy regular exposure to good quality |
| research studies suggest that a generous | | | | sunlight, the intake of 400 IU (10 mcg) of |
| intake of vitamin D may be a significant | | | | vitamin D as part of a multi-vitamin and |
| mitigating factor. | | | | multi-mineral supplement is recommended. For |
| | | | the over 65s, those with less than optimal |
| Blood levels of vitamin D have also been | | | | liver or digestive health, those living in |
| shown to be inversely correlated with blood | | | | less advantageous climates and those who |
| pressure, and some research suggests that | | | | spend the majority of their time in indoor |
| high dose supplements of vitamin D of (1,600 | | | | occupations a supplementary dose of a further |
| IU per day) may help this, although orthodox | | | | 400 IU, for a total of 800 IU is strongly |
| medicine, as ever, is cautious about | | | | advised. |
| definitively acknowledging any direct causal | | | | |
| link. | | | | For maximum effect, however, vitamin D |
| | | | supplementation should be always be combined |
| The traditional view was that adequate | | | | with adequate dietary calcium - supplemented |
| supplies of vitamin D can be synthesised in | | | | if necessary to achieve an intake of 1,000 - |
| the skin upon its exposure to sunlight. But | | | | 1,200 mg per day of this essential mineral. |