There is evidence to suggest that 90% of the UK population is deficient in vitamin D (less than 30nmol/ml) and that 5-20% are severely deficient (less than 10nmol/ml). Vitamin D is known as the “sunshine vitamin” because our bodies require direct sunlight on the skin to manufacture it. This is our main source of the vitamin. Only about 20% is obtained from the diet. A combination of poor British summers and use of sunscreens, i.e. lack of exposure to the sun, is the main factor in this epidemic of deficiency. Cholecalciferol (vitamin D3) is the form made by the body, and which is present in some foods, such as oily fish. Ergocalciferol (vitamin D2) is the most common form present in foods. Cholecalciferol (vitamin D3) is believed by most to be the most effective form, particularly when correcting deficiency and this can be bought as a supplement and is available as vegetarian source. Vitamin D is fat soluble, so is best taken with fatty or oily food for maximum absorption, hence the tradition of taking cod liver oil, which contains both.
The recommended daily requirement is a minimum of 600iu per day for those aged between 1 and 70 and 800iu for the over 70s. The daily requirement from birth to age 1 is 400iu. To correct deficiency a daily intake of at least 1000iu for ages 1-18 then 1500-2000iu for all ages above that would be required. Those with severe deficiency may require much higher doses, but this should be done with the guidance of their GP. Vitamin D can be toxic in high doses, although recently it has emerged that much greater doses can be taken than previously thought.