This is one vitamin that the most Australians will probably never fall short of as it is formed by our bodies when our skin is exposed to sunlight. However, the damaging effects of too much sun on our skin has been well documented. A normal person's day to day sun exposure is quite adequate.
One of the interesting things about Vitamin D is the way it functions almost in the same way as a hormone, targeting the kidneys and intestines as well as the pancreas, brain, skin and bones. It is a fat soluble vitamin.
This vitamin -
- regulates absorption of calcium from the gut,
- is especially important in maintaining the balance of calcium and phosphorous in bone formation,
- maintains an adequate calcium level in the blood.
While rare, deficiencies can lead to misshapen bones (known as rickets in children) and weakening of the bones in adults. Identified through bone pain and spasms in the muscles attached to the bones.
Vitamin D is produced by the body when it is exposed to sunlight. Good food sources include fatty fish (sardines, tuna, salmon, mackerel, herrings), butter, table margarine, fish liver, oils, nuts and egg yolk.
Deficiencies can occur among people who are housebound as well as those in countries where the winters are long and cold and skin lacks exposure to the sun. If you rarely go outside during the day or are an older person living in an aged care facility, you need a good dietary source of vitamin D.
Vitamin D is the most potentially toxic of all vitamins. Too much allows the body to absorb excessive calcium, causing calcium deposits in the spleen and kidneys.
There is no RDI for vitamin D in Australia because most people have exposure to sunlight and their vitamin D state is linked to this. In the UK, only 10 micrograms per day is recommended for house bound adults. Large doses of cod liver oil can provide toxic levels of this vitamin. Toxic effects are seen with just 45 micrograms in children or 250 micrograms per day in adults. Children and infants are even more sensitive to over-dosing.