The vitamin D series

There are two closely related types of vitamin D, D-2 and D-3. Both are fat-soluble and therefore can be stored in the body. Vitamin D2 (calciferol) can be taken in by eating any balanced diet including vegetables and milk products. Vitamin D3 is produced in the skin by biological processes that are best catalysed by sunlight. Sunlight helps to metabolize calcium–cholecalciferol in the skin into usable vitamin D. We need sunlight to produce enough vitamin D to keep us going through the UK winter, with its low light intensities (even worse in the polar regions). Low vitamin D concentrations can lead to bone disorders including bone loss, osteoporosis and rickets. The health service does give guidelines on how much D is needed.
It suggests vitamin supplements to various people, including the elderly, who often stay indoors or cover up from sunlight. Approximately 10 mg of vitamin D is required each day. Even a small amount of sunlight is beneficial, but it must be of sufficient duration or intensity to be fully effective. In tropical zones the sunlight is sufficient to be absorbed through thin clothing. In northern climates it is probably best to absorb sunlight directly. In more recent times Britain, being in northern latitudes, has had an influx of residents from sunnier areas such as the

Caribbean and Asia. In some instances the colour of their skin (developed to protect them from very hot sunshine) has prevented them absorbing enough sun to effectively make enough vitamin D. Some people have skin discolouration as a result of lack of vitamin D and a supplement might be suggested.
Some hip bone deformities can be due to this problem and in some communities it is noticed that older Asian women now living in the UK have a pronounced ‘roll’ in their walking and movement due to this deformity. For such communities a vitamin supplement is often suggested.
Vitamin D is necessary to allow the body to metabolize calcium and phosphorus effectively. Independent of the formation of vitamin D, it must be emphasized that excessive uptake of UV sunlight can lead to abnormal skin cell division and the possibility of skin cancer.