There are not many foods which naturally contain vitamin D. Vitamin D is taken up in three ways by the body. The first, and most natural, way is through the UV rays of the sun and consuming food which contains small amounts of vitamin D such as whole milk, fatty fish, fish liver oils, beef liver, cheese, and egg yolks. The second is through vitamin D supplements which can be purchased at a variety of health shops and, the third, through food and drink which has been fortified with vitamin D.
In the early 1900s, there were many children who suffered from weak and brittle bones which almost always developed into rickets. At the same time, scientists were doing research on calcium and phosphorus and drawing links between these minerals and strong teeth and bones. It was evident that the children who suffered from rickets, which was an alarming 80% of children in the Boston area in the 1900s, were not receiving enough calcium and phosphorus.
The children, however, were consuming ample amounts of calcium and phosphorus-rich milk. This lead scientists to the realisation that merely consuming calcium and phosphorus is not enough to ensure the growth of strong teeth and bones.
It was in 1922 that Dr E.V. McCallum discovered that calcium and phosphorus absorption in the body relied solely on vitamin D. This is to say that vitamin D is responsible for the body’s ability to take up calcium and phosphorus from food and drink and that a lack of vitamin D would result in these minerals simply passing through the body. The children of the 1900s were deficient in vitamin D which left their bones weak and brittle.
Vitamin D is a fat soluble vitamin, and fat is responsible for the body’s ability to absorb vitamins and minerals. This brings about a modern debate about the best type of milk to drink. Half and skim milk variations take up most of the milk aisle of any supermarket and health enthusiasts encourage the consumption of low-fat varieties over full-fat options but the only milk which naturally contains any level of vitamin D is full-fat milk.
All milk is fortified with vitamin D, so every type has a similar vitamin D content. However, if a diet does not contain enough fat then vitamin D will not be absorbed into the body which means that calcium and phosphorus absorption will be inhibited. In the same way that calcium and phosphorus pass through the body when there is a lack of vitamin D in the system, vitamin D will also simply pass through the body if there is not enough fat in the system.
In fact, it has been proven that people who consume full-fat milk can lose weight and lower the risk of vitamin A, D, K, and E deficiency. The shift in the 20th century to saturated fats being public enemy number one resulted in the plummet of whole milk sales and an increase in half and skim milk varieties, however, recent years have shown a shift back to whole milk options due to the realisation that people need fats in their diet. The most effective way to ensure that one is consuming enough vitamin D, and absorbing it effectively, is to consume whole milk over half and skim varieties.