Vitamin D is a fat-soluble vitamin which acts like a
hormone, regulating the formation of bone and the absorption of calcium and phosphorus from the intestine.
It helps to control the movement of calcium between bone and blood, and vice versa. In infancy and
childhood, deficiency of vitamin D causes the deformed bones characteristic of rickets, while in adults a
lack of the vitamin causes a softening of the bones known as osteomalacia. Deficiency is seen more often in
northern countries, or where tradition dictates that the body is well covered by clothes, such as in parts
of the Islamic world. An excess of the vitamin can cause loss of appetite, weight loss, nausea, headache,
depression and deposits of calcium in the kidneys.
Vegans and Vitamin D
Vegans usually obtain vitamin D from the action of
sunlight on the skin or by taking fortified foods such as soya milk, margarine and vitamin supplements
which are made from yeast or other fungi. Fortified vegan products contain D2 (ergocalciferol). Foods with
naturally occurring vitamin D are, however, usually animal derived containing the vitamin D3
The most significant supply of vitamin D (for
omnivores as well as vegans) comes from the action of ultra-violet B light on sterols in the skin. Most
people, including infants require little or no extra from food when regularly exposed to sunlight when the
sun is high in the sky. Bright sunlight is not necessary; even the sky shine on a cloudy summer day will
stimulate formation of some D in the skin, while a short summer holiday in the open air will increase blood
levels of the vitamin by two or three times the amount.
The effective light wavelength - ultra-violet B (UVB,
290-315 nanometers in wavelength) - is not present in winter sunlight between October and March in
countries above latitude 52 degrees north, which includes most of Britain. Winter time supplies of vitamin
D depend on the previous summers exposure creating adequate stores in the liver, or on dietary