Vitamin D is a fat soluble vitamin and is needed to regulate calcium and phosphate in the body. Calcium and phosphate are needed to keep teeth, bones and muscles healthy. As most people know, vitamin D is synthesised in our skin when it is exposed to sunlight. Sadly most of us don't get enough between September and April as there isn't enough UV exposure in the U.K. Vitamin D is also found in just a few foods; though it is difficult to get enough vitamin D from food alone. Sources include, Oily fish (salmon, sardines, mackerel, herring, fresh tuna), red meat, liver, egg yolk and fortified foods (fat spreads, soy/almond milks and some cereals).
If you live in the U.K , you should take a daily supplement containing 10ug or 400IU of Vitamin-D during the winter months. You can either buy a tablet or you can buy a spray for under your tongue. If you aren't often outside, if you wear clothes that cover up most of your skin or wear SPF, the World Health Organisation suggest you should take a supplement daily all year round.