Our bodies obtain vitamin D (which, strictly speaking is a steroid hormone) from two sources, our diet and from the action of sunlight on our skin which drives the natural production within the body. If we all had plenty of sun then we would have plenty of vitamin D, but in reality we do need to obtain some from our diet, particularly during the winter months and particularly in the elderly as the body's ability to manufacture vitamin D declines with age.

Indeed as many as 60 percent of the UK population is vitamin D deficient and low levels have been linked to serious health problems in later life.