Two years ago, the news broke that vitamin D may prevent colon cancer.

At the time, I realised that this type of news report would sow much confusion among the general public because the natural reaction of the man on the street would be to start taking vitamin D supplements in an attempt to prevent colon cancer.

The danger of excessive intakes of vitamin D also crossed my mind.

Since then, a variety of scientific articles have been published on the subject. These may shed some light on how much vitamin D the average South African requires and how this vitamin can be obtained.

Sources of vitamin D
The two main sources of vitamin D are oral ingestion of foods (particularly those that are fortified with vitamin D, such as most brands of margarine and some brands of packaged milk) or vitamin supplements, and exposure of the skin to sunlight, which causes the body to manufacture its own vitamin D.

Research has shown that western diets are often deficient in vitamin D, with elderly people ingesting considerably less vitamin D than required. However, the use of vitamin D supplements is associated with potential overdosing and interactions that can occur between vitamin D and other nutrients.

It is, however, relatively easy for most people in sunny South Africa to expose their skins to sunlight for short periods every day to make their own vitamin D.

It is estimated that an exposure lasting 20 minutes a day should be sufficient for most individuals to produce adequate vitamin D supplies in their bodies.

Slightly longer exposure times are required for people with black or brown skins because darker skins are not as efficient in producing vitamin D as white skins.

Persons with white skins should also not overdo sun exposure as this is linked to skin damage, eye damage, and the potential development of skin cancer or melanoma.

Link between vitamin D and cancer
According to German researchers in an article published recently, a large number of studies have confirmed that vitamin D deficiency is linked to the development of colon, prostate and breast cancers.

Interestingly, there is an association with distance from the equator (high sun exposure) and an increased incidence of breast, colon, prostate and ovarian cancer. In other words, these cancers occur more commonly in those countries where exposure to the sun is less likely due to inclement weather (e.g. the Scandinavian countries and Northern Europe).

In addition, research studies have found that exposure to sunlight (which produces more vitamin D in the body) improved the outcome and increased the survival rate for some cancers.

Researchers believe that vitamin D is a potent hormone that can regulate cell growth, thus having a beneficial effect on cancerous tissue.

It is well known that a serious vitamin D deficiency causes rickets in children and bone deterioration (a condition called osteomalacia) in adults.

Vitamin D may also help against autoimmune diseases, cardiovascular disease and to control cholesterol. The latter function is due to the fact that the body produces vitamin D from cholesterol, thus lowering cholesterol levels.

It is known that cholesterol levels increase in populations in winter in those countries that have little sunlight, and may explain geographical differences in the incidence of coronary heart disease.

Daily vitamin D requirement
An important question that now needs to be answered is: "How much vitamin D is required to protect us against cancer and other diseases?"

In the USA, nutrition authorities recommend an RDA of 200 International Units (IU) or 5 microgram.

In view of the new research findings, some scientists now estimate that we may require up to 1000 IU or 25 microgram of vitamin D a day to prevent bone fractures, protect us against certain cancers and obtain other health benefits.

This recommendation is being questioned by other experts who fear that vitamin D overdose may ensue if the general population start taking massive doses of vitamin D.

Solutions
In view of this controversy, the most sensible advice is to eat foods that are rich in vitamin D or have been fortified with added vitamin D, namely: egg yolk, liver, milk, margarine and soy milk (check the labels of milk, margarine and soy milk to see if these products contain added vitamin D).

And expose your skin to the sun for 20 minutes a day or slightly longer if you have a dark skin. Full body exposure to sunlight can produce as much as 10 000 IU or 250 microgram of vitamin D in your body and because vitamin D is a fat-soluble vitamin, it can be stored in the liver for future requirements.

Don't overdo sun exposure as this can lead to skin problems and even cause melanoma (skin cancer) if you have a light skin.

If you do decide to take a vitamin D supplement, it is prudent to not exceed 100% of the RDA (check on the label), i.e. 200 IU or 5 microgram per daily dose.

As South Africans, we are in the lucky position to be able to use our sunny climate to provide most of our vitamin D requirements, which should be protective against certain cancers, bone deterioration and even lower our cholesterol levels slightly. – (Dr Ingrid van Heerden, DietDoc)

Reference:
(Gilchrest, BA. (2005). J Am Acad Dermatol,52:868-76; Reichrath J et al (2006). Clin Dermatol: Retinoids & Other Treatments, 13-15.)

- May 2006