Called the sunshine vitamin (because your body makes all it needs with enough sunlight), vitamin D is essential for bone health and may slow the progression of arthritis. It's also believed to strengthen the immune system and possibly prevent some cancers.
What it is?
Technically a hormone, vitamin D is produced within the body when the skin is exposed to the ultraviolet B (UVB) rays in sunlight. In Australia and New Zealand, spending a short period in the sun each day supplies all the vitamin D your body needs, but people confined indoors may not get enough sun to generate adequate vitamin D, and so need to obtain this vitamin from food or supplements.
What's more, the body's ability to manufacture vitamin D declines with age, so vitamin D deficiencies are common in older people. But even young adults may not have sufficient vitamin D stores. One US study of nearly 300 patients (of all ages) hospitalized for a variety of reasons found that 57% of them did not have high enough levels of vitamin D. Of particular concern was the observation that a third of the people who obtained the recommended amount of vitamin D through diet or supplements were still deficient. This finding suggests that current recommendations for vitamin D may not be high enough.
What it does?
The basic function of vitamin D is to regulate the levels of calcium and phosphorus in the blood, helping to build strong bones and healthy teeth.
Studies have shown that vitamin D is important in the prevention of osteoporosis, a disease that causes porous bones and thus an increased risk of fractures. Without sufficient vitamin D, the body cannot absorb calcium from food or supplements – no matter how much calcium you consume. When blood calcium levels are low, the body will move calcium from the bones to the blood to supply the muscles – especially the heart – and the nerves with the amount they need. Over time, this reallocation of calcium leads to a loss of bone mass.
Scientists are continuing to discover more about the functions of vitamin D in the body. Some studies suggest that it's important for a healthy immune system. Others indicate that it may help to prevent prostate, colon or breast cancer. One study found that adequate vitamin D slowed the progression of osteoarthritis in the knees, although it did not prevent the disease from developing in the first place.
- Helps the body to absorb calcium.
- Promotes healthy bones.
- Strengthens teeth.
- May protect against some types of cancer.
- Soft gel.
- Overuse of vitamin D supplements can result in elevated blood levels of calcium, leading to weight loss, nausea, and heart and kidney damage.
- Reminder: If you have a medical condition, talk to your doctor before taking supplements.
How much you need?
There is no RDI for vitamin D in Australia or New Zealand, as enough is made when the skin is exposed to sunlight. However, people who are confined indoors are recommended to get about 400 IU (10 mg) daily from their diets.
If you get too little:
A vitamin D deficiency can harm the bones, causing rickets in children and increasing the risk of osteoporosis in adults. A deficiency can also cause diarrhoea, insomnia, nervousness and muscle twitches. (The likelihood of a child in Australia or New Zealand developing rickets is remote.)
If you get too much:
Although your body effectively rids itself of any extra vitamin D it makes from sunlight, overloading on supplements may create problems. Daily doses of 1000 – 2000 IU over six months can cause constipation or diarrhoea, headaches, loss of appetite, nausea and vomiting, heartbeat irregularities and extreme fatigue. Continued high doses weaken the bones and allow calcium to accumulate in soft tissues, such as the muscles.
How to take it?
As little as 30 minutes of early morning or late afternoon sunlight on your face, hands and arms two or three times a week can supply all the vitamin D you need. But some studies show that it's preferable not to be wearing sunglasses or sunscreen for this period. Both the skin and the retina of the eye may need a brief period of exposure for vitamin D to be produced. (Between the hours of 11 a.m. and 3 p.m., however, you should always cover up and protect yourself with a hat and sunscreen.) If you're over the age of 50, if you don't get outdoors much or if you always wear sunscreen, you might want to consider vitamin D supplements. Many experts recommend 400 – 600 IU a day for people over the age of 50 and 800 IU for those over the age of 70. For younger adults, 200 – 400 IU a day is probably sufficient.
Guidelines for use:
Supplements can be taken at any time of day, with or without food. Most daily multivitamins contain up to 400 IU of vitamin D. It is also often found in calcium supplements.
Fatty fish, such as herring, salmon and tuna, are rich in vitamin D.
Facts and Tips
- To be effective, supplements must contain vitamin D3 (cholecalciferol), not vitamin D2 (ergocalciferol).
- Calcium and vitamin D supplements slowed bone loss and reduced the incidence of fractures in 176 men and 213 women over the age of 65 participating in a recent US study. They took 500 mg of calcium and 700 IU of vitamin D a day for three years.
- Vitamin D may help to prevent colon cancer. In a study of 438 men, researchers found that those with colon cancer had lower blood levels of vitamin D than those who did not have the disease. Across the board, men with the highest vitamin D intake had the best chance of avoiding colon cancer. More study is needed to confirm this finding and to see if the risk is the same for women.