Vitamin D is obtained through the diet, and depending on sun exposure is also produced and stored in the body. Dietary vitamin D is found in fortified food, such as milk and butter, fish and sun-dried shitake mushrooms.

Traditionally, the primary function of vitamin D3 has been to assist in the development, growth and mineralisation of a healthy skeleton through its role in calcium metabolism. Recent findings however have shown other benefits of vitamin D3, such as playing a vital role in maintaining the immune and nervous systems, a healthy cardiovascular system and cardiac muscle, healthy skin, kidney health and muscle strength. Vitamin D is also required for healthy cell differentiation, particularly in the prostate gland.

The body’s ability to metabolize vitamin declines with age, as does the ability of the skin to produce vitamin D3. Supplementation may also help reduce the risk of falls and therefore fractures.

Dosage and safe prescribing

Optimal blood levels of vitamin D are between 30–60 ng/mL. Suggested supplementation is normally 1000IU of D3 per day, depending on current blood status. Vitamin D occurs in two forms; cholecalciferol (D3) is produced by the action of sunlight on skin and is also found in animals and fish (e.g. cod-liver oil); and ergocalciferol (D2) is found in a very limited range of foods. When taken as a supplement, D3 is regarded as the most important dietary form and is identical to the form produced in the body, whereas D2 is a synthetic form found often in inferior supplements.