Vitamin D is a fat-soluble (dissolves in fats and oil) vitamin with many positive health effects. In humans vitamin D is produced on the skin when in contact with ultraviolet rays of sunlight.

Everyone needs vitamin D but some need it more crucially such as children below 3, pregnant and lactating women, people with limited sun exposure, elderly people, people at risk for osteoporosis, dark skinned and vegans.

There are two types of Vitamin D. Vitamin D3 (cholecalciferol) is produced by the skin through absorbing sunlight. Vitamin D2 (ergocalciferol) is produced from plants and mushrooms. Vitamin D3 is 87 per cent more effective in raising Vitamin D levels. The sun’s rays provide ultraviolet B (UVB) energy. The sun-skin contact kicks off the process of producing pre-vitamin D and then in the liver and kidney to start making vitamin D.

Body cannot absorb calcium it ingests without vitamin D. Calcitriol, the active form of vitamin D circulates as a hormone, regulating the concentration of calcium and phosphate in the bloodstream and promoting the healthy growth and remodeling of bone. Without vitamin D body starts to use calcium from bones making them porous and weak.

Vitamin D prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis. Vitamin D also helps maintain normal blood levels of phosphorus, another bone-building mineral. Vitamin D tells the body whether to store these minerals in bones or take them from there for the vital body functions.

Most people get the vitamin D they need through sunlight exposure. 20 minutes of exposure to sunlight produces up to (10,000 to 20,000 IU) 250 µg of Vitamin D in the skin. This is equivalent to serum calcidiol (25-OH D) level of 100-200 nmol/l. It can also be obtained through the diet, but very few foods naturally contain vitamin D. These foods include fatty fish, fish liver oil, and eggs. Also meat and cheese contain small amounts. Most dietary vitamin D comes from fortified foods, such as milk, juices, yogurt, bread, and breakfast cereals. Vitamin D can also be obtained through dietary supplements.

Sometimes the deficiency can be caused by other factors than lack of sun or proper diet. Some medications (antiseizure drugs, glucocorticoids), metabolic conditions like obesity or malabsorption like in Crohn’s disease can cause lower than needed levels of Vitamin D.

Yes it can be toxic in very high doses but it is extremely rare. As defined by EFSA (European Food Safety Authority), daily maximum intake of vitamin D for adults is 100 micrograms (4000 IU) and for children up to 10 years 50 micrograms (2000 IU) and for infants 25 micrograms (1000 IU). With recommended daily doses there is no risk.

The easy blood test measures the concentration of 25-hydroxyvitamin D3, or 25(OH)D, the precursor produced by the skin and converted in the body to vitamin D. Levels are expressed either in nano grams in milliliter (ng/mL) or in nanomoles in liter (nmol/l).

If one is over age 70, has darker skin, or lives at a northern latitude (far away from equator) or not regularly exposed to the sun or wear sunscreen, are at high risk of D-deficiency and should go for testing. People who have malabsorption problems or take medications that interfere with vitamin D activity (for example, glucocorticoids) should consider it as well.

The cost for testing at health clinics is approximately 40 euros.

With aging populations, the cost of treating vitamin D deficiency related diseases is rising globally at unbearable rate. The cost of treating osteoporosis symptoms alone is estimated to double in next ten years and quadruple in forty years. Global research for 17 countries in Europe extrapolates potential cost savings to healthcare systems of up to € 187 billion if the problem of vitamin D deficiency is addressed.

The IOF (International Osteoporosis Foundation) support an increase in recommended vitamin D intake levels in Europe. They call for evidence-based proposals of 1,000-2,000 IU per day, especially for risk groups such as the elderly and postmenopausal women: “Vitamin D supplementation offers an effective, inexpensive and safe public health strategy to reduce 20% of falls and fractures, including those at the hip, in a growing senior segment of the European population. This is an enormous public health benefit we could implement now.”

There are initiatives on country level, regionally and globally to help raise awareness and to introduce vitamin D to large populations for the micro- and macro-level benefits.

Doubling vitamin D levels seems to be the most cost-effective way to reduce global mortality rates, states a study published in the European Journal of Clinical Nutrition. Latest big news from January 2012 is that England’s chief medical officer backs (free) vitamin D supplements. England’s chief medical officer Dame Sally Davies has begun campaigning to the English medical fraternity that certain population groups like under-5s should take vitamin D supplements. Also EU is frequently addressed with requests demanding educational campaigns, research and technical measures to increase vitamin D intake on population level.

The European Food Safety Authority EFSA has given a positive scientific opinion which states that an adequate intake of vitamin D plays an essential role in human health, and in particular, bone health.