Vitamin D, also known as the “sunshine vitamin”, is a fat soluble vitamin that we get from sunlight exposure, from food and from dietary supplements. Vitamin D is critical to maintain bone health as it controls calcium absorption and maintains the correct levels of phosphorous in the blood.
Beyond your bones, vitamin D is also a key factor in cell growth and health, immunity and inflammation. A real jack-of-all-trades, research is even showing that the right levels of vitamin D may help in the prevention of cardiovascular disease, diabetes, obesity and certain cancers.
Read: The miracle of vitamin D
How is it made?
The body produces vitamin D when you soak up the sun, or more scientifically when the skin is exposed to UVB rays. This allows the inactive vitamin D to convert to its pre-active form.
But that’s not all; the liver then converts this form of vitamin D to be transported safely in the blood, before it is finally converted to its biologically active form, known as calcitriol. It is interesting to note that almost all the many millions of cells that make up the body have a specialised vitamin D receptor that can activate vitamin D.
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What’s in a name?
Vitamin D2 (ergocalciferol) is the form of Vitamin D found in non-animal sources, such as some mushrooms.
Vitamin D3 (cholecalciferol) is the pre-vitamin form found naturally in some food sources such as salmon, pilchards and egg yolks.
25-hydroxyvitamin D3 (calcidiol) is the form found in the blood. Also referred to in scientific terms as 25(OH)D3.
1,25-dihydroxyvitamin D3 (calcitriol) is the biologically active form of vitamin D. Also referred to in scientific terms as 1,25(OH)2D3
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The Recommended Dietary Allowance (RDA) for vitamin D in individuals aged 1–70 years is 600 IU. After the age of 70 years the RDA increases to 800 IU daily.
Sunlight exposure: We don’t want to encourage excessive sun tanning, but the sensible and safe recommendation for optimal vitamin D status is to expose the hands, arms and legs (20% of the body) for 5–10 minutes, between the hours of 10am–3pm, three times a week. Use your lunch break at work or tea break to step outside, get some fresh air and obtain your vitamin D quota for the week.
Read: The sun and vitamin D
Darker skinned individuals, the elderly and obese individuals may benefit from extra supplement of vitamin D, due to the following:
- Melanin pigment absorbs UV radiation and decreases the rate of activation of Vitamin D. Therefore, darker skinned individuals may require 5–10 times more sun exposure to produce the required amount of vitamin D.
- The precursors required for vitamin D production decline with age. As a result, someone over the age of 60 years produces 75% less Vitamin D than someone of 20.
- Vitamin D3, a fat soluble vitamin can be stored in fat cells known as adipose tissue. In obese individuals Vitamin D is so efficiently stored that it is no longer available for use in bone metabolism and regulation.
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Food sources with Vitamin D
Fatty fish such as salmon, tuna, mackerel, sardines and pilchards, as well as fish liver oils such as cod liver oil are some of the best sources of vitamin D3. Smaller amounts are found in liver, beef, cheese and egg yolk.
Because few natural food sources of vitamin D exist, most of our pre-active vitamin D in the blood comes from sunlight exposure rather than from food. If those gorgeous drops of golden sun are limited – such as during winter or in the Northern Hemisphere where sunlight is scarce, vitamin D must come from supplements.
It makes no difference whether vitamin D comes from the sun or from a supplement, either D2 or D3. Because Vitamin D is a fat soluble vitamin, it should be eaten or taken in supplement form, together with a meal or snack that contains fat.
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Image: Softgel supplement capsules from iStock
1. Mahan L, Escott-Stump S & Raymond J. (2012) Krause’s Food and the Nutrition Care Process. Chapter 3; pg. 63-70.
2. Webb, D. (2012) Vitamin D and Cancer. Today’s Dietitian Volume 14 no 10, pg 58-61.
3. Holick MF, Gordon CM. (2011) The Hormone Foundation’s Patient Guide to Vitamin D Deficiency. J Clin Endocrinol Metab. 96(7):1-2.
The dietitians from Nutritional Solutions are Health24's expert team of registered dietitians.