Vitamin D deficiency is a major global public health problem that concerns all age groups, in addition to individuals residing in countries with low latitude, where it was generally assumed that ultraviolet radiation was adequate enough to prevent this deficiency, and in industrialised countries, where vitamin D fortification has been implemented for a long period of time.
Vitamin D deficiency is widely prevalent all over the world, especially among young girls and women in the Middle East. Recent studies reported 50 per cent of pregnant women in the UAE being deficient. In neighbouring Saudi Arabia, a study found 59pc of healthy schoolchildren to be deficient and 28pc insufficient in vitamin D.
The major sources of the fat-soluble vitamin D for most humans are casual exposure of the skin to solar ultraviolet B radiation and from dietary intake.
According to the guidelines, 25-30 minutes of sun exposure between 9am and 11am twice a week to the face, arms, legs or back without sunscreen is usually enough to help boost vitamin D intake. Due to concerns about skin cancer, many people avoid direct sun exposure and depend on dietary sources for their vitamin D requirement. Most diets, however, are low in vitamin D. In particular vegan and vegetarian diets. For instance, a study reported that the prevalence of vitamin D insufficiency in vegans was higher than in omnivores (73pc versus 46pc).
The richest sources of vitamin D include fish liver oils, oily fish, egg yolk and wild mushrooms. But even those foods can vary highly in their vitamin D content. This is clearly demonstrated by the fact that levels of vitamin D in fish can vary significantly both between and within species and according to whether they are wild or farmed. For example, farmed salmon was shown to have approximately a quarter of the vitamin D levels of that found in their wild counterparts. In particular the top food in vitamin D (μg/100g) content are: eel (25.6), pike-perch (24.6), herring (15.4), salmon (12.4), egg yolk (7.8), tuna (7.2), cod (7.0), egg (2.8), liver, beef (0.8) and butter (0.3). Mushrooms supply in particular vitamin D2. Among the vitamin D-rich foods, only fish, such as salmon, are considered to be one of the best sources that affect directly the vitamin D serum levels.
Unfortunately, nowadays only few foods are fortified with vitamin D. Fortified foods are those to which one or more essential nutrients have been added, whether or not it is normally contained in the food, for the purpose of preventing or correcting a demonstrated deficiency. Typical vitamin D fortified foods include milk, yogurt, breakfast cereals and margarine and most recently fortified orange. It is important that you consult your healthcare provider, especially if you are vegan or vegetarian.
Dr Simone Perna is Assistant Professor in the Department of Biology, College of Science, at Bahrain University