Earlier this year, Public Health England released new guidelines on the intake of vitamin D supplements, as it was found that 20% of adults and around 17% of children are vitamin D deficient. Although vitamin D is present in many foods, it is in such a small amount that we simply cannot get enough from diet alone. Exposure to sunlight is the main way to reduce the risk of vitamin D deficiency, however modern lifestyles often confine people to staying indoors and the risk of skin cancer has led many people to use sunscreens, preventing the absorption of UV radiation which normally activates the precursor of the active vitamin.
It is now recommended that from the age of 1 year upward, people should take 10micrograms of vitamin D each day. This is advised throughout the whole year for individuals who do not get adequate exposure to sunlight in the summer months and for those who do, supplements should be taken in the autumn and winter months.
Vitamin D plays a major role in calcium homeostasis in the body. Calcium is important for muscle contraction, blood clotting, transmission of nerve impulses and bone formation, so its levels need to be tightly controlled in order to keep these processes occurring normally. Vitamin D deficiency can result in rickets and osteomalacia, in which bone cannot be mineralised due to a lack of calcium, causing it to become weak.
The first image bellows shows the synthesis of vitamin D, from the precursor 7-dehydrocholesterol. 90% of this biomolecule is converted into cholecalciferol by UVB radiation and only 10% is consumed through the diet. Cholecalciferol then undergoes a further series of reactions until the active form of vitamin D, calcitriol, is produced.
The second email below illustrates the synthesis of vitamin D a little differently and demonstrates its function in the body.
To see the images in full, please click on the links below to download the files.