Not enough sun - In order to maintain adequate levels of vitamin D, we need to spend some time in the sun, in a sensible way. The Australian Cancer Council recommends a few minutes of exposure to sunlight on most days in summer outside peak UV periods (10am to 3pm). In the winter months, most people will need about two to three hours of sun exposure spread over a week, particularly in the southern parts of Australia.
Sun protection - Broad-spectrum sunscreen lotions protect the skin against UVA and UVB rays. However, the body requires UVB rays for the conversion of vitamin D3 in the skin.[1,21] While it is important to protect our skin from the risk of skin cancers and premature ageing, it is also important to remember that we do require some sun exposure (safe sun exposure) to make vitamin D3. Alternatively, supplementation is a great way to get your vitamin D without sun exposure.
Dark skin - If you are dark-skinned, the pigments in your skin reduce UV penetration so you’ll need more sun exposure (three to six times more) to make sufficient amounts of vitamin D3.
Ageing - Ageing decreases the body’s ability to manufacture vitamin D from sun exposure.[1,2] What's more, as we get older, we don’t seem to get as much vitamin D from the foods we eat. If you are over 50 years old, you are more likely to be vitamin D deficient due to a reduced ability to manufacture vitamin D in the skin, and possibly reduced intake from your diet.
Medications - Certain medications can impact our vitamin D levels:
Some anticonvulsants that are used to treat epilepsy can block the body's ability to convert vitamin D into its storage form. Patients who take anti-epileptic medication have been found to be deficient in vitamin D.
Statins, which are generally prescribed to reduce high cholesterol levels, may also block the cholesterol-based precursors in the skin that are required for vitamin D production. Research has found that patients on statin medication with low vitamin D elves were more likely to suffer from muscle pain. It is therefore important to maintaining adequate vitamin D levels while taking statins will reduce your likelihood of developing statin-induced side effects such as muscle pain. Maintaining adequate levels of vitamin D is also important in general for supporting a healthy cardiovascular system.
Fat binding agents, which block fat to help people manage their weight, can also upset the body’s vitamin D levels. Vitamin D is a fat-soluble vitamin which means that it needs a small amount of fat in order to be taken up by the body. Without fat from the diet, patients may have difficulty absorbing dietary vitamin D.
Gastrointestinal problems - If you have gastrointestinal problems such as Crohn's disease or coeliac disease, or suffer from malabsorptive conditions, then you may be having trouble absorbing vitamin D from food. Any condition which has an effect on the gastrointestinal wall may affect the absorption of vitamin D.