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Vitamin D

Vitamin D

The role of sunshine vitamin in bone health

Vitamin D is synthesised in the skin following exposure to sunlight, hence its association with the name "sunshine vitamin". Vitamin D is an important nutrient because one of its major roles is to ensure we have the right amounts of calcium circulating in our bodies. It does this by influencing how much calcium we absorb from the foods we eat. That's why vitamin D and calcium are very important for building and maintaining strong, healthy bones.

Vitamin D benefits

Vitamin D has received extensive coverage and new research shows that optimum intake levels may be far higher than the current Nutrient Reference Value (NRV) of 5μg/day. The benefits are wide and varied and include contribution to the maintenance of normal bones and teeth; contribution to the maintenance of normal muscle function; contribution to the normal function of the immune system and healthy inflammatory response, and contribution to the absorption of calcium and phosphorus , the maintenance of normal blood calcium concentrations and regulation of blood sugar levels. Recommended Dietary Allowances bellow are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies.

Age (mg/day) (IU/day)
Birth to 12 months 10 mg* 400 IU*
1-70 years 15 mg 600 IU
70+ years 20 mg 800 IU
*Adequate Intake (AI)    
Source: Food and Nutrition Board, 2015    

Sources of Vitamin D

Vitamin D is a fat-soluble vitamin that when consumed or made in the skin, can be stored in the blood and body fat, for several months. The best source is sunlight, which your body uses during the sunny months to manufacture the vital vitamin in your skin. You should try to get ten minutes of sun exposure to your bare skin, once or twice a day without sunscreen whilst taking care not to burned. Get outside for approximately 10-15 minutes (depending on skin type) between May and September so that your body can produce enough vitamin D to help see you through the winter months. How much sunshine we are exposed to, and therefore the amount of vitamin D we produce in our skin, is primarily determined by where we live; for example some countries in the northern hemisphere have more cloud cover and longer winters and so see less of the sun -so their inhabitants produce less vitamin D. However, it is very important to avoid over-exposure resulting in sunburn, as we are all aware of the damaging effects of the sun.

Note: You don't need to actually tan your skin to get the benefits and after a few minutes you should protect your skin from the sun. The amount of sun exposure needed will depend on skin colour (people with darkler skin require longer sunlight exposure times to generate an equivalent amount of vitamin D), the time of year, time of day, whether the skin is covered (with clothing or sunscreen) and location are several factors that influence photosynthesis and bioavailability of vitamin D. In summer, protecting the skin with a hat, clothing and sunscreen is recommended to avoid sunburn and skin damage. This is particularly important for babies, infants and children.

Food

If you live in a northern climate where sun exposure isn't a year-long guarantee, many foods will provide you some of the daily intake of vitamin D. Although small amounts of vitamin D are found naturally in some foods, such as fatty fish, liver and eggs, as well as in some fortified dairy products, most adults are unlikely to obtain more than 10% of their vitamin D requirement from dietary sources

Food Vitamin D (mg) Vitamin D  (IU)
Cod liver oil (1 tbsp) 23.1 924
Mackerel (grilled, 100g) 8.8 352
Salmon (grilled, 100g) 7.1 284
Sardines (canned in brine, 100g) 4.6 184
Tuna (canned in brine, 100g) 3.6 144
Egg, hen (average size, 50g) 0.9 36
Liver, lamb (fried, 100g) 0.9 36
Source: FAO/WHO, 2004    

Supplements

To prevent vitamin D deficiency in people who receive less than optimal sun exposure or not getting enough from the foods, vitamin D supplementation is recommended. As vitamin D and calcium deficiencies are more common in older people who are housebound or in residential care, vitamin D supplementation in combination with adequate calcium intake (preferably from diet), is recommended to reduce the risk deficiency. While there are plenty calcium and vitamin D supplements to choose from, speak to your doctor or pharmacist for trusted advice on what to buy and how much to take.

Who is most at risk of vitamin D deficiency?

Vitamin D deficiency is possible if you:
  •  Live in a northern climate
  •   Have naturally dark skin
  •   Deliberately avoid sunlight
  •   Wear clothing that covers most of the skin
  •   Spend long periods indoors because of disability or illness
  •   Have a medical condition or take medication that affects vitamin D levels

Vitamin D deficiency can have many effects. A very obvious sign is soft bones in both children and adults. In children, this commonly leads to bowed legs. In adults vitamin D deficiency can be one of the causes for osteoporosis. Deficiency can also lead to a weakened immune system, more inflammatory and autoimmune diseases, weak muscles, diabetes and some recent research suggests that D levels have a relationship with cognition in older adults. Excessive exposure to sunlight does not lead to excessive vitamin D levels in the body while large doses of vitamin D supplements should be taken with care as they can cause unpleasant and possibly toxic side effects. If any of the above risk factors apply to you, you should consult your doctor or health care professional for further advice.