It is the vitamin that is actually a hormone, made naturally by the body from fat under the skin in response to sunlight.
And, astonishingly, more than half the British population don’t get enough, with one in six severely deficient in Vitamin D by early spring.
Evidence suggests this may raise the risk of a host of problems from bone-thinning, heart disease and cancer to diabetes and even depression. The answer, experts agree, is taking a supplement throughout autumn and winter.
So just why are these pills – made from sheep’s wool and mushrooms – so vital to our health?
WHY WE DON’T GET ENOUGH VITAMIN D
We need ten to 15 minutes of direct sunlight on unprotected skin several times a week from May to September to make enough Vitamin D to see us through the winter. Darker skins may need longer as the pigmentation doesn’t allow such efficient production, and fairer skin less time.
Outside these months, the sun is at the wrong angle to produce the right wavelength of ultraviolet light, and no Vitamin D is produced.
‘People are so aware of the dangers of UV damage that they often avoid it and we’re especially careful of children, because of the link between early sunburn and skin cancer. In October, our levels of Vitamin D should still be acceptable, assuming we have gone out in the sun during the summer,’ says Dr Elina Hypponen of the Medical Research Council’s Centre of Epidemiology for Child Health.
‘But Vitamin D is stored for only between one and two months in the body. From now on, levels start to drop and by January almost everyone will have below optimum levels. We’re starting at a disadvantage this year after an appalling summer. I recommend taking supplements now.’
WE ALL NEED MORE OF THE SUNSHINE VITAMIN
The body needs Vitamin D to absorb calcium, which is essential for bone health. Deficiency increases the risk of the bone-thinning disease osteoporosis and fractures by up to 60 per cent and can also cause osteomalacia, a bone-softening condition.
‘There is evidence it may slow the progression of cancer,’ says John Monson, professor of Endocrinology at The London Clinic.
And Dr Hypponen says: ‘There are links between Vitamin D deficiency and raised risk of heart disease, cancer and diabetes. Studies show keeping levels up may help prevent seasonal infections such as colds.’