What is vitamin D?
Vitamin D refers to a group of related fat-soluble vitamins and is vital for good health throughout our lives. It plays many roles in our bodies including assisting calcium absorption and aiding in bone mineralisation.
There are two significant forms of Vitamin D which are important for humans. One is vitamin D3 (colecalciferol) which is formed in our bodies when sunlight penetrates our skin. A small amount of vitamin D3 is also available from a few animal foods. The other is Vitamin D2 (ergocalciferol) and is found in a small range of foods derived from plants.
Sources of vitamin D
The main source of Vitamin D for Australians is from exposure to sunlight. It’s important to realise that although we live in a generally sunny country, many things can affect the amount of exposure to UV radiation and vitamin D synthesis in the body. These include – season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen. Also, UVB radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D.
The factors that affect vitamin D levels make it difficult to provide general guidelines on adequate amounts of sun exposure. Individuals with limited sun exposure need to include good sources of vitamin D in their diet or take a supplement to achieve recommended levels of intake.
Vitamin D is also available through a small number of foods. The best food sources of vitamin D are fatty fish (sardines, herring, mackerel, tuna and salmon), milk (especially milks with added vitamin D), and vitamin D fortified soy drinks, margarines and dairy blend spreads. Red meat and eggs contain very small amounts of vitamin D. It is important to know that dietary sources alone rarely provide enough vitamin D to maintain adequate levels.
Vitamin D tablets, capsules and liquids are available to help you increase your vitamin D intake. Supplements are available in many forms including tablets, capsules and liquids. The strength will vary but vitamin D is commonly available in a 1000IU dose for adults.
Benefits of vitamin D
Vitamin D affects several areas in the human body. Importantly, Vitamin D aids the absorption and use of calcium and phosphorus from the small intestine and assists bone mineralisation. This is a major function of vitamin D.
Pregnancy and lactation are important times to ensure that adequate calcium and vitamin D intake is met. The developing baby is dependent on the mother for adequate vitamin D nutrition, which is important for healthy development of the skeleton.
The need for vitamin D continues into childhood where growing children require Vitamin D for optimal bone mineralisation especially during times when sunlight exposure is limited.
In the elderly additional dietary vitamin D may be required as the ability of the skin to make vitamin D with exposure to sunlight decreases with age.
In addition to bone health, vitamin D helps support muscle function by supporting muscle tone and strength. Research also suggests that vitamin D may help maintain a healthy immune system.
How Much vitamin D is adequate?
There is no Australian RDI for vitamin D, only adequate intake is advised. Table 3 shows vitamin D adequate intake amounts.
|Age Group||Adequate Intake|
|Children 1-18 years||5 mcg (200IU)|
|Men 19-50 years||5 mcg (200IU)|
|Men 51-70 years||10 mcg (400IU)|
|Men >70 years||15 mcg (600IU)|
|Women 19 – 50 years||5 mcg (200IU)|
|Women 51 – 70 years||10 mcg (400IU)|
|Women > 70 years||15 mcg (600IU)|
|Pregnancy 14 – 50 years||5 mcg (200IU)|
|Lactation 14 – 50 years||5 mcg (200IU)|
|Table 3. Adequate Intakes for vitamin D|
How can I determine my vitamin D level?
It is difficult to know if your body’s level of vitamin D is sufficient because so many factors can influence its status. To obtain a reliable result you will need to visit your GP and arrange to have a simple Vitamin D blood test. Your GP will be able to discuss the results with you and organise treatment accordingly.
What to ask for at your GP
If you are concerned about your body’s vitamin D levels speak to your GP. He or she will be able to arrange a simple blood test to determine your D vitamin status.
If your levels of are insufficient, your GP may also be able to suggest ways of obtaining more vitamin D including supplement recommendations.
Nutrient Reference Values for Australia and New Zealand. Vitamin D. Australian Government, National Health and Medical Research Council, https://www.nrv.gov.au/nutrients/vitamin-d