One would think that most people who live in the tropics will not be lacking in Vitamin D given that there is sunshine all year round.
The surprising thing is that a large majority of my patients who live in the tropics do not have sufficient Vitamin D; the main reason being that most of them live in modern cities and spend most of their time in offices.
While it is a well-known fact that Vitamin D deficiency leads to rickets, a bone disease in the young, less is known about the need for Vitamin D in adults.
Functions of Vitamin D
Vitamin D is routinely produced by our skin upon exposure to the ultraviolet B (UVB) light of the sun.
The Vitamin D in the body behaves like a hormone, and beyond the commonly known effect of Vitamin D on the absorption of calcium from the gut, it has multiple effects at the cellular level with diverse functions such as preventing abnormal cells from multiplying in the large intestine, helping to control the blood pressure in the kidney and helping to control the blood sugar in the pancreas.
Vitamin D and bones
For a long time, doctors were dispensing calcium tablets to postmenopausal women routinely until studies published a few years ago showed that excessive calcium intake, through calcium supplements, was linked to increased incidence of stroke and heart attacks.
This was considered to be due to the increased deposition of calcium in the walls of the arteries of the heart and brain resulting in hardening, degenerative changes and narrowing of the arteries.
There was also an increased incidence of stones in the kidneys. In the light of these findings, the focus shifted towards ensuring that Vitamin D levels were adequate. Vitamin D when consumed gets converted to an active form that regulates calcium absorption in the body.
Despite the findings of the dangers of excessive consumption of calcium, the mass media is inundated with advertisements on the "goodness" of regular consumption of high calcium milk and calcium fortified foods.
The current recommendation for those with a healthy diet is to avoid calcium supplements and to take Vitamin D instead for bone health.
Studies have shown that elderly individuals with low Vitamin D levels are more likely to develop fractures and higher doses of Vitamin D intake can reduce the likelihood of fractures.
An analysis of more than 40,000 elderly individuals, combining the data from 12 studies on the prevention of fracture, found that vitamin D intakes of about 800 IU per day decreased hip bone and non-spine fractures by 20 per cent, while lower dosages (400 IU or less) did not provide any protection.
In addition, adequate Vitamin D intake can potentially increase muscular strength, thereby reducing the likelihood of falls, a common problem for the elderly.
An analysis from the data of multiple trials found that this benefit was seen only in those taking 700 to 1000 IU of Vitamin D daily and was not seen in those on lower doses.
Vitamin D and the heart
Multiple studies, including the Health Professional Follow-Up Study which examined the vitamin D levels in close to 50,000 healthy men for 10 years, found a twofold risk of heart attack in those with low vitamin D levels.
Studies have also shown that lower Vitamin D levels are seen in those with heart failure, high blood pressure and stroke. There is some evidence that Vitamin D may have a role in regulating blood pressure and preventing artery damage.
Vitamin D and diabetes risk
Vitamin D levels also have an association with increased incidence or likelihood of developing diabetes mellitus, a major risk factor for heart disease.
Diabetics are commonly found in populations who have low Vitamin D levels or who avoid sunshine. Vitamin D supplementation of 800 IU/day was associated with lower incidence of diabetes requiring oral medication.
A child living in Finland has about 400 times increased risk of developing diabetes requiring insulin than a child in Venezuela. A 30-year study on more than 10,000 Finnish children found that those on vitamin D supplementation since infancy had about 90 per cent risk reduction of developing diabetes as compared to those not on supplements. Other smaller European studies have also showed a similar result.
Vitamin D and cancer
The difference in the incidence of large intestine cancers between those who live in the north and those who live near the equator have led physicians to examine the relationship between Vitamin D and large intestine cancer.
Studies have shown that there is an association between cancer of the large intestines and low Vitamin D levels. However, there is no available data yet to demonstrate that Vitamin D consumption will lower cancer risk.
Sunshine versus Vitamin D supplementation
If you are applying sunblock to your skin, unless the sunblock blocks both ultraviolet A (UVA) and UVB light from the sun, you may end up only blocking UVB but not UVA.
In that case, the Vitamin D forming effect of the sun may be absent but the skin damaging rays of the sun will still persist.
Hence, if you apply sunblock regularly on your exposed skin or are a vegetarian, you are likely to have low Vitamin D levels. Food content of Vitamin D is generally low, though fish and eggs have better Vitamin D content.
In case you start deciding to get more sunshine on your skin , be aware that sunburns and the regular use of tanning machines will increase the incidence of skin cancers especially melanomas, the most serious skin cancer.
This is especially so in those who have pre-existing moles, freckles and immediate family members with skin cancers. Melanomas also seem to be more aggressive and are associated with higher death rates in those with Vitamin D deficiency.
In case you start loading yourself with large amounts of Vitamin D, you may want to know that recent analysis of combined data from multiple trials (meta-analysis) were not able to demonstrate any significant benefits.
One of the major drawbacks of meta-analysis is that it combines data from populations who have different base levels of Vitamin D and are of diverse backgrounds, and the studies used for analysis have different aims and different trial designs.
The main practical point from these results is that one should not be consuming Vitamin D excessively if the body has adequate Vitamin D levels.
In an article on Vitamin D published this month in the highly regarded Circulation Journal, the authors recommend that if you are deficient in Vitamin D and are at risk of heart attack or stroke, one should aim to achieve normal Vitamin D levels by either appropriate Vitamin D supplementation or increased sunshine exposure.
Sunshine exposure is usually less likely to damage the skin if it is in the early morning or late afternoon.
The take home message is that Vitamin D deficiency should be avoided but excessive Vitamin D supplementation has not been shown to be beneficial.
Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia (a journal of the British Medical Journal Publishing Group); chairman, scientific advisory board, Asia Pacific Heart Association; and honorary professor and senior medical adviser, Peking University Heart Centre.
This article was published on April 19 in The Business Times.
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