Updated 20 May 2013

Vitamin D

Vitamin D (also called calciferol) is a fat soluble vitamin which acts as a hormone, which means that it’s made in one place in the body but used elsewhere.

Vitamin D (also called calciferol), a fat soluble vitamin, acts as a hormone, which means that it’s made in one place in the body but used elsewhere.

Most of the vitamin D your body uses is made under your skin when you’re exposed to the sun, but you also get it from food.

What it does for you

Vitamin D helps ensure strong bones by increasing the rate that minerals such as calcium and magnesium are deposited into bones. It’s also crucial for the absorption of calcium from food.

But that's not where its benefits stop.

Research links vitamin D deficiency with an increased risk of death, especially from cardiovascular disease.

Scientists don't know how low levels of vitamin D contribute to cardiovascular problems or other causes of death. But study after study has shown that vitamin D plays a key role in human immunity.

Vitamin D deficiency has also been associated with several types of cancer.

Which foods have vitamin D?

Cod liver oil (capsules or liquid form), fatty fish such as herring, mackerel, sardines and salmon, as well as trout and tuna, eggs and cheese.

How much vitamin D do you need?

The current adequate intake (AI) is 5 microgram per day for both male and female adults, although people over the age of 50 need to take between 10 and 15 microgram per day.

While no recommendations can be made as yet, the latest research shows that most of us probably need more of the vitamin. Note that the tolerable upper intake limit (UL) is 50 microgram per day.

It is also advised that you spend 10 to 15 minutes per day in the sun (up to 40 minutes if you are dark-skinned) to allow your body to produce vitamin D naturally.

How much vitamin D is too much?

Combining cod liver oil capsules and vitamin D supplements can result in excessive intake. The upper safe limit is 50 microgram per day.

Signs of vitamin D deficiency

Rickets, once common in children of poorer families who lived in areas of little sunshine, is more rare now. It was caused by poor diets in breastfeeding mothers and resulted in soft, curved bones, particularly in the legs.

Breastfeeding mothers who take 10 microgram of vitamin D daily can avoid the problem. People over 65 should take the same amount.

Other signs of vitamin D deficiency include muscle pain, weak bones, low energy and fatigue, lowered immunity and symptoms of depression and mood swings.

If you live in a country with abundant sunshine, like South Africa, you may believe that your body has sufficient Vitamin D levels. However, if you spend most of your daytime indoors and use sun protecion, you may need to look for other sources of vitamin D.

Others who may need extra vitamin D include people with dark skin (the more skin pigment someone has, the less efficiently the body can make vitamin D); people with certain conditions (such as liver diseases, cystic fibrosis and Crohn’s disease); and people who are obese or have had gastric bypass surgery.

New research on vitamin D

Researchers have found conclusive evidence that vitamin D cuts the risk of breast cancer in women; and another study has shown that giving children supplemental vitamin D helps prevent them from developing type 1 diabetes later on.

Low blood levels of vitamin D appear to increase the risk of heart attack and stroke, according to several preliminary studies. And people with low vitamin D levels may face an increased risk for peripheral artery disease, which occurs when arteries in the legs become narrowed or clogged with fatty deposits, reducing blood flow to the legs.

Researchers have also found that patients diagnosed with colorectal cancer who had abundant vitamin D in their blood prior to diagnosis were less likely to die during a follow-up period than those who were deficient in the vitamin.

But contrary to findings from earlier studies, it appears that rather than high vitamin D levels decreasing the risk of prostate cancer, they in fact elevate the risk of aggressive disease. However, researchers emphasise that these findings might have occurred by chance.

Recent Australian research also showed that low levels of vitamin D are associated with the loss of cartilage in the knee joints of older individuals. Cartilage loss is the hallmark of osteoarthritis.

Two new studies from the US have uncovered evidence that low levels of vitamin D could lead to poor blood sugar control among diabetics and increase the risk of developing metabolic syndrome among seniors. (Metabolic syndrome is a grouping of health risk factors, including high blood pressure, abdominal obesity, abnormal cholesterol levels and high blood sugar.)

Asthmatic children with relatively low vitamin D levels in their blood may have a greater risk of suffering severe asthma attacks than those with higher levels of the vitamin, a new study from Harvard Medical School suggests. Whereas there is no evidence that sufficient vitamin D levels protect kids from moderate asthma symptoms, children with vitamin-D "insufficiency" are more likely to have an asthma attack that requires a trip to the hospital, the research team has found.

A team of Danish scientists recently discovered how vitamin D is crucial for the actual activation of the immune system. "Low levels of Vitamin D suffered by around half the world's population may mean their immune systems' killer T cells are poor at fighting infection," the team reported in the journal Nature Immunology. They also warned that the problem was getting worse as people were spending more time indoors. Even in countries with abundant sunshine, people spend most of their daytime indoors and no longer get enough sunshine to help produce Vitamin D.


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