Vitamin D strengthens bones and muscles and is therefore essential for the prevention of osteoporosis. Recent studies have also demonstrated the important role of vitamin D in cardiovascular health and for the prevention of diabetes and some forms of cancer. The human body is capable of synthesising vitamin D through solar exposure. In people who spend time outdoors regularly, the skin produces 80 to 90% of the total vitamin D requirement. The remaining 10 to 20% needs to be introduced through dietary intake. Foods like salmon, herring, mackerel, liver and egg yolk are rich in vitamin D.