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 usually contain animal derived vitamin D3 (cholecalciferol). (There is one form of D3 that is derived from lichen and suitable for vegans, which is marketed as Vitashine).
Recently, United States Department of Agriculture (USDA) scientists reported that mushrooms that had been exposed to ultraviolet B light for 5 minutes had very high levels of vitamin D, close to 3,500 International Units (IU) in a 1-cup serving.4 These vitamin D-containing mushrooms are expected to be commercially available in the next few years and will be a plantbased source of vitamin D.
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, w Winter time supplies of vitamin D depend on the previous summers exposure creating adequate stores in the liver, or on dietary sources.
Requirements For Vitamin D
It has been found that bone loss in post menopause women occurs mostly in the winter due to falling levels of vitamin D products in the blood. A winter intake from fortified foods or supplements is strongly recommended to promote bone health. Winter intakes of about 15 ug (micrograms) per day appear to be appropriate to prevent bone loss.
If we lived as we evolved – in the open nearer the equator – we would synthesise vitamin D from sunlight equivalent to 100 ug (micrograms) or more per day and dietary intake would be irrelevant.