THE PROBLEM WITH VITAMIN D
It is very difficult to get enough vitamin D from your diet alone.
Some foods like oily fish, egg yolks and margarine contain some vitamin D, but not much. For example: wild salmon gets vitamin D from the food chain, but farmed salmon contains practically no vitamin D. Nonetheless, to get even close to enough vitamin D, you would have to eat 5-7 portions of Salmon per week.
Some foods are fortified with vitamin D, for example some cereals, but the amount added is very small. It is not enough to satisfy our daily vitamin D requirement.
It has been shown that in winter time humans cannot make any vitamin D above the latitude of Atlanta Georgia in the USA, because UVB rays do not reach these latitudes between approximately October and March, this includes the whole of the UK. In winter, supplementation is vital to get enough vitamin D.
Modern lifestyle is heightens deficiency risks. Nowadays we spend most of our time in offices and cover up our bodies more. There are fewer opportunities to expose our skin to sunlight and to make vitamin D. Additionally, groups who cover up their bodies for religious reasons are also at very high risk of deficiency.
All year round, supplementation is important for most of the population and especially at risk groups. Pregnant and breastfeeding mothers, infants in their first year of life and darker skinned populations are at increased risks.