|
Headlines linking vitamin D and cancer caused a run on the vitamin in UK pharmacies over the Christmas holiday period. The stories were triggered by a meta-analysis of 63 studies of colon, breast, bowel and prostate cancer published in the American
Journal of Public Health. Most of these
studies showed that a greater intake of vitamin D from the diet or supplements,
or both, protects against cancer. The authors suggested that “vitamin
D supplementation could reduce cancer incidence and mortality at low
cost, with few or no adverse effects”.
Vitamin D receptors have been found in more than 30 different tissues
or organs and it is now well established that the active form of the
vitamin is made in many different tissues from where it is secreted and
used in a paracrine fashion. Patient laboratory work has shown that vitamin
D is essential for the normal differentiation of many specialised cells
and has a vital role in apoptosis — the programmed death of cells
that have finished their useful life. When there is insufficient vitamin
D in the body not only are cells more likely to develop incorrectly but
they are also less likely to be weeded out by apoptosis. Such rogue cells
are now thought to be the first stage in the development of cancer.
Altogether some 18 or more different cancers occur more frequently in
northern than in southern states of the US and many of them have a similar
north-south distribution in Europe and Japan. This “ecological” evidence,
as it is called, is not definitive but, considered together with all
the other evidence from work with cells and animals and from case-control
studies on a smaller number of cancers, it will convince many people
that vitamin D has a major role in preventing many cancers.
Rickets, osteomalacia and osteoporosis are the most obvious results of
vitamin D deficiency. But in recent years evidence has accumulated to
suggest that vitamin D insufficiency, or lack of exposure to the sun,
has a role in many other chronic diseases: multiple sclerosis, hypertension,
diabetes (types 1 and 2), metabolic syndrome, heart disease, inflammatory
bowel conditions, polycystic ovary disease, menstrual problems, some
infections and dental decay.
If ever there was such a thing as a panacea vitamin D would qualify before
anything else. After all, it is the only vitamin that cannot be obtained
in sufficient quantity simply from a healthy diet, however hard you try.
The best dietary source of vitamin D in the UK is margarine, which is
mandatorily fortified with it. The second best source used to be breakfast
cereals but, recently, Kellogs stopped fortifying many of its cereals
in order to comply with requirements in other EU countries while maintaining
economic production runs. This ought to be sending waves of panic through
Government but it has been done quietly and nobody appears to have noticed
yet.
About 5 per cent of the population obtain a useful supplement of vitamin
D from multivitamin products, cod liver oil and vitamin D formulations
of various kinds. But most of these products provide vitamin D in modest
amounts of around 200IU per day.
The optimum daily intake of vitamin D from all sources (food, supplements
and sunshine) is now believed to be between 3,000 and 5,000IU per day.
Most people in the UK, however, obtain well under 1,000IU per day — even
during summer — and as a result some 60 per cent of adults in the
UK have levels of vitamin D that are insufficient (serum calcidiol <50nmol/L)
and some eight per cent are grossly deficient (serum calcidiol <25nmol/L).
For the time being at least the sun is our best source of vitamin D,
as it has been since man first came to northern Europe and evolved a
white skin that gave the best chance of using the thin spring and autumn
sun that occurs in that part of the world. For six months of winter the
sun is not strong enough in Europe for any vitamin D to be made in skin.
However for some 20 years we have been told by government or Cancer Research
UK (CR-UK) that exposure of the body to the sun during the four hours
in the middle of the day risks skin cancer, that we should cover up,
seek shade and put on sunscreen 20 minutes before going out. This is
the CR-UK SunSmart programme, which has been imported from Australia
and is totally unsuited to the British climate.
Greater lifetime exposure to the sun, however, seems to protect against
melanoma — as it does against other cancers — although it
is important to avoid burning. CR-UK’s Government-sponsored SunSmart
programme appears to be giving us the wrong advice and over the years
may have increased the overall risk of cancer, including melanoma. This
is a tragic mistake for such an important and distinguished charity.
It must be remedied quickly so we do not have yet another summer when
the public is told to cover up and avoid the sun around midday. The middle
of the day is a convenient time to sunbathe and when the sun is best
able to provide vitamin D, which we now know is so vitally important
for health. |
The
Pharmaceutical Journal