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.

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.

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.

Click here to view a complete list of AI and UL values.

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.

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.

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

Researchers have found "conclusive evidence" that vitamin D cuts the risk of breast cancer in women; and another study has "clearly shown" that giving small 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 attacks, according to the results of a study involving middle-aged and older men. And people with low vitamin D levels may face an increased risk for peripheral artery disease (PAD), which occurs when arteries in the legs become narrowed or clogged with fatty deposits, reducing blood flow to the legs.

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. But researchers emphasise that these findings might have occurred by chance.