Causes of Low Vitamin D Levels: High Risk Groups

The primary means of getting adequate vitamin D is via sunlight exposure, and so deficiencies are more frequent in areas that receive less sunlight. Some of the recent studies on the link between low vitamin D levels and cancer found that the lowest levels were in countries at higher latitudes, with shorter days and longer winters.

Along these lines, people with darker skin may also be at greater risk, as their skin acts like sunblock and absorbs less light, especially when they move to higher latitudes where sunlight is less direct. One study published in 2007 found that African refugees in Australia were 40% more likely to develop low vitamin D levels.

In theory, sunblock itself may reduce vitamin D levels, but in practice it doesn’t seem to have this effect, per a study published in the Archives of Dermatology in 1995, which looked at 113 adults and found that there was no significant difference in vitamin D levels in the sunblock group compared to the placebo group.

Elderly people are also at greater risk, partially because they do not absorb nutrients as well and partially because they don’t spend as much time outside. Elderly people should take vitamin D supplements, and the US RDA for the elderly has recently been bumped up to 800 IU per day.

Outside of the above, causes of low vitamin D levels are pretty rare. There are a few rare genetic disorders that can cause it, such as autosomal dominant hypophosphatemic rickets. And genetic variation in populations can lead to lower or greater levels as well, as was found in a study performed on Northern Europeans, who despite the low levels of sunshine had higher levels of vitamin D than those living in Central and Southern Europe.

While many people probably do not get the optimal dose, causes of low vitamin D levels are rare and only in certain high risk groups. If you don’t fall into one of the risk groups, you probably aren’t in any danger of deficiency. However, D is relatively safe to take and there is some (preliminary) evidence that it may help reduce the risk of heart disease and certain cancers. If you don’t get much sunlight and you don’t eat much fish or fortified milk (the main food sources of D), you might want to consider adding a 600 to 800 IU supplement to your daily routine. Just keep it well below 4000 to avoid any toxic effects.