Scientific evidence is accumulating that shows that vitamin D not only maintains the calcium balance and prevents bone deformation (rickets, osteomalacia and osteoporosis), but has many other functions in the human body.
Recent research reported in the Arbor Clinical Nutrition Updates (June 2006) indicates that adequate levels of vitamin D may counteract calcification of the arteries, prevent stroke and reduce high blood pressure.
A Japanese study found that in renal patients on dialysis, who are generally at risk of vitamin D deficiency because of renal failure, vitamin D supplementation significantly reduced the risk of death from heart disease.
Another study conducted in the USA with more than 8000 adults, showed that subjects who had high vitamin D levels were significantly less likely to develop metabolic syndrome than subjects who had low vitamin D levels.
Metabolic syndrome is a cluster of conditions or derangements of normal metabolism, which include obesity (particularly abdominal obesity), insulin resistance or type II diabetes, hypertension, and arteriosclerosis.
The third study mentioned in the latest edition of the Arbor Clinical Nutrition Updates (June 2006), found that patients with congestive heart failure responded positively to a vitamin D supplement of 50 microgram a day, which they received together with a calcium supplement.
The link between an adequate vitamin D intake or adequate levels of vitamin D in the body, and heart disease, hypertension and stroke was evident for some time before specific research studies were performed.
Researchers noticed that people living in countries far from the equator, where exposure to sunlight (which permits the formation of vitamin D in the human body) is low, were more prone to heart disease and hypertension than people living in countries where sun exposure is high.
A link between seasons, vitamin D levels and heart disease was also identified. Winter in the northern hemisphere, when sunshine is limited to a few hours a day and the cold prevents exposure of bare skin to sunlight, is associated with a higher incidence of heart disease and hypertension than the summer months.
Although these so-called epidemiological studies can point the way towards a link between a nutrient (in this case, vitamin D) and certain diseases, well-controlled scientific studies are required before such findings can be proven.
At present, the studies on vitamin D and heart disease, hypertension and stroke, are still in the early phase and much more research will be necessary to clearly define this link between heart disease, hypertension, stroke and vitamin D.
What does this mean to South Africans?
South Africans are particularly susceptible to heart disease, hypertension and stroke – all three of which claim thousands of lives every year.
White South Africans and urbanised black South Africans are prone to heart disease, while hypertension and stroke are reaching epidemic proportions amongst black South Africans.
Although many factors play a role in these diseases (e.g. genetic predisposition, unhealthy diets, lack of exercise, smoking), evidence from other parts of the world indicate that either having an adequate dietary intake of vitamin D, or manufacturing enough vitamin D by exposing the skin to at least 20 minutes of sunlight a day to enable the body to manufacture its own supply of vitamin D, may be important in preventing heart disease, hypertension and stroke.
"But, we have such abundant sunshine in South Africa, that there shouldn't be a problem," I hear you say. This may be true for South Africans who spend some time every day in the sun, but what about those of us who sit all day in offices or in schoolrooms, and no longer work or play in the sun?
In addition, people with darker skins or those who cover their bodies completely with clothing (e.g. Muslim women or swaddled babies), are less likely to produce sufficient vitamin D in their bodies.
This year's winter is particularly cold and most South Africans are bundled up with only their faces and hands exposed to the ultraviolet rays of the sun – thus most of us are not manufacturing much vitamin D at the moment.
Tips to ensure adequate vitamin D
The simplest way to ensure that you are making some vitamin D is to expose your body to the sun for about 20 minutes a day, particularly in winter. This should also apply to infants and young children.
If you are home- or office-bound and never see the sun, it may be advisable to take a vitamin D supplement at least every second day.
According to the Recommended Dietary Allowances, we need 200 International Units (IU) or 5 microgram of vitamin D a day. Don't exceed these levels when taking supplements, because excessive intakes of vitamin D can also be harmful.
We need additional research to identify exactly how vitamin D influences heart disease, hypertension and stroke. In the meantime, however, we can make sure that we get some sun exposure every day, that we eat foods rich in vitamin D (egg yolk, liver, and vitamin D-enriched milk, margarine and soy milks), and, if necessary, take a vitamin D supplement about three times a week. – (Dr Ingrid van Heerden, DietDoc, January 2009)
(Arbor Clinical Nutrition Updates (2006). Vitamin D & cardiovascular disease. June 2006, No 254:1-3).