Vitamin D is produced naturally in the body when UV rays come in contact with the surface of the skin. This is the reason it is referred to as the sunshine vitamin. One of the main functions of this vitamin is calcium and phosphorous absorption.  Through these it plays a role in bone growth and remodelling and along with calcium, prevents osteoporosis in old age.  It also helps fight many chronic illnesses such as diabetes, and some kinds of cancers. This makes the vitamin a very important one to be able to obtain.
The main source of Vitamin D is the sun as previously mentioned. However, a lot of factors come into play with sun exposure. Season of the year, time of day, cloud cover, smog, and skin melanin content, are among the factors that affect UV radiation exposure and therefore vitamin D synthesis. Along with that, direct exposure to the sun is required for its synthesis, through windows is not enough. Along with the sun, other sources of the vitamin are from food intake. Fatty fishes like Salmon and Tuna, egg yolk, milk (which is fortified with vitamin D in Canada).
Although it may seem like the vitamin is available in much abundance and can be obtained quite easily, this does not seem to be the case for many Canadians. Stats Canada has found that 10% of the population does not have enough for proper bone health.  This is not seem an alarming number as a whole. However, when certain factors are taken into consideration, Muslim women are at high risk to be included in that 10 percent.
Most Canadians that have enough vitamin D tend to have lighter skin, since the decreased melanin content allows them to be able to absorb more UV rays. Darker skin pigmentation makes it harder to be able to synthesize the vitamin since less UV radiation is absorbed into the skin.  Girls who choose to wear the hijab are also at risk of low vitamin D levels. This is mainly because of lack of direct contact with sunlight. A girl, who wears hijab, hardly goes out into the sun with arms, back or legs exposed. The face also is at times shielded by the hijab or with sunscreen all putting Muslim women at risk for low vitamin D levels. 
Symptoms of deficiency include constant fatigue, headaches, muscle weakness, depression, and it can also cause ricketsia in children. These can affect one’s day to day life, leading to an inability to accomplish what one wants to during the day, this inability can also increase the chances of falling into depression. These along with the fact that the Vitamin is absolutely necessary for proper bone health suggest that adequate levels are very necessary to maintain .
If you are Muslim and a hijabi and get constant headaches and can not go on through the day like you used to be able to, it is very likely that you are vitamin D deficient. Supplements for the vitamin and a slightly modified diet can easily fix the problem and getting checked is just a matter of visit to the doctor’s.
1. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
2. Cranney C, Horsely T, O’Donnell S, Weiler H, Ooi D, Atkinson S, et al. Effectiveness and safety of vitamin D. Evidence Report/Technology Assessment No. 158. University of Ottawa
3. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988;67:373-8.