Vitamin D plays an important role in bone health. It helps our body absorb and use calcium. Without this vitamin, our bones may lose large amounts of calcium and become more fragile. Children need vitamin D to build strong, healthy bones, and adults need it to maintain high bone mass density. Studies show that people with vitamin D deficiency are at increased risk of fracture.

Severe vitamin D deficiency is now very rare in the Western world. If it does occur, it may cause a very serious condition called osteomalacia in adults and rickets in children. These disorders are entirely different from osteoporosis.

Recommended Daily Intake of Vitamin D

According to international scientific guidelines:

• Adults under 50 years of age need 400–800 IU (International Units) of vitamin D daily in their diet.
• Adults over 50 years of age need 1000 IU of vitamin D daily.

There are two types of vitamin D supplements: vitamin D2, also called ergocalciferol, and vitamin D3, also known as cholecalciferol. Older studies suggested that D3 was a better option than D2, but more recent research has shown that there is no substantial difference. The maximum permitted amount of vitamin D is 4000 IU per day.

Sources of Vitamin D

There are three ways for our body to receive vitamin D:

• Exposure to sunlight
• Food
• Dietary supplements (and corresponding medicinal preparations)

Your skin produces vitamin D when it is exposed to the sun’s ultraviolet radiation (UVB). Your body is able to store it and use it later. The amount produced in this way depends on many factors, such as age, skin colour, time of day, season, and altitude. People with fair skin produce greater amounts of vitamin D than those with darker skin. Also, those living in regions far from the equator have less time of exposure to sunlight (for example, Northern Europeans compared with Mediterranean populations). In addition, there are people, mainly older individuals, who because of mobility problems cannot easily leave their homes and are therefore exposed to even less sunlight. Window glass and air pollution further reduce the chances of sunlight reaching our skin.

Also, because of the justified concern about skin cancer, especially in countries such as ours, the use of sunscreen is very common. These creams may block ultraviolet radiation from reaching our skin by as much as 95%. This fact should not discourage the use of sunscreen, especially in individuals at increased risk (fair-skinned people). It is better to be protected from skin cancer, even if this means that, if necessary, you may need to take vitamin D supplements.

Foods Containing Vitamin D

Unfortunately, there are very few foods with a high vitamin D content. It is rather difficult to obtain all the vitamin D you need daily from natural foods alone. Fatty fish, such as swordfish, trout, salmon, and tuna, contain significant amounts of vitamin D.

There are also foods and products that are artificially fortified with vitamin D, such as dairy products, soy milk, juices, and cereals. Look at the product labels for information about their vitamin D content.

One serving of vitamin D-fortified milk (about one glass) contains approximately 25% of the recommended daily amount of vitamin D, that is, 100 IU.

Vitamin D Supplements

Many people cannot meet their daily vitamin D needs from food and sunlight exposure alone. These individuals need to take additional dietary supplements.

Before purchasing such a product, check the labels of any other preparations you may already be taking in order to see whether they contain vitamin D. Many multivitamins and dietary supplements contain this vitamin. You should also calculate the amount you receive from food.

Depending on your age, calculate the dose you need from the supplement accordingly. Do not forget to subtract the amount of vitamin D you receive from other sources (for example, foods or calcium supplements).

Vitamin D supplements can be taken at any time of the day. They do not need to be taken at the same time as calcium supplements, nor do they require the acidic environment needed for calcium absorption. Your body stores the vitamin and uses it when needed.

If you are unsure which supplement is appropriate for you, ask your doctor or pharmacist.

Testing Vitamin D Levels in the Body

Vitamin D levels can be checked with a simple blood test. People who get an adequate daily intake of vitamin D do not need to undergo this test.

However, there are also people who cannot meet the recommended daily vitamin D intake. When this continues for a long time, the body’s vitamin D stores become depleted and problems begin to appear. These individuals should undergo testing to determine their vitamin D levels.

Examples of people who may be at risk of vitamin D deficiency include:

• People who do not often go outside their homes and, when they do, wear clothes that cover most of their body
• People living in institutions (e.g. nursing homes, hospitals)
• People with mobility problems who are essentially confined to their homes
• People with malabsorption syndromes, such as coeliac disease and inflammatory bowel disease
• People taking medications that affect vitamin D levels in the body, such as certain antiepileptic drugs
• People with very dark skin
• People who are overweight or obese
• Older individuals with specific risk factors

Discuss with your doctor whether you need to be tested for vitamin D. The test measures the levels of 25-hydroxyvitamin D (often written as 25(OH)vitD). It should not be confused with the test for 1,25(OH)vitD.

If the test you have undergone shows that you have vitamin D deficiency, ask your doctor what you should do. Some doctors, especially when the patient’s vitamin D levels are very low, initially prescribe large amounts of vitamin D (even in injectable forms) in order to replenish the body’s stores quickly, and then proceed with daily administration to cover the ongoing daily requirements. Repeating the test after 3 months is recommended in order to assess the outcome of treatment.