Vitamin D
Vitamin D plays a key role in assisting calcium absorption from food, ensuring the correct renewal and mineralization of bone tissue, and promoting a healthy immune system and muscles. In children, severe vitamin D deficiency results in delayed growth and bone deformities known as rickets, and in adults, a similar condition called osteomalacia (a 'softening' of the bones, due to the poor mineralization). Milder degrees of vitamin D inadequacy can lead to a higher risk of osteoporosis, and an increased likelihood of falling in older adults whose muscles are weakened by a lack of the vitamin.
Vitamin D is made in our skin during the summer months from exposure to the sun's ultraviolet B rays. In children and adults, casual exposure of the face, hands and arms for as little as 10-to-15 minutes a day outside peak sunlight hours (before 10am and after 2pm) is usually sufficient for most individuals. Vitamin D can also be obtained from food, and dietary supplements, and these sources increase in importance during the winter months for populations in northern latitudes (when no skin synthesis of vitamin D takes place), and for the elderly. The elderly are particularly vulnerable to vitamin D deficiency as they are often housebound or living in nursing homes with little exposure to the sun, and because from the 60's onwards, the skin's capacity to synthesize vitamin D decreases. Other factors such as the use of sunscreens, a greater degree of skin pigmentation, and an increase in indoor occupations and pastimes also reduce the opportunity for skin synthesis of vitamin D. Recommendations for vitamin D intake by age group are shown in the table below.
Food sources of vitamin D are rather limited, and include oily (or fatty) fish such as salmon, tuna, sardines and mackerel, egg yolk and liver. In some countries, fortified foods specifically labeled as such, including milk and other dairy foods, margarine, and breakfast cereals, are viable options.
Recommended vitamin D intake
by age group, both as international units (IU) and micrograms| Age group | RNI* (IU/d) | RNI (μg/d) | ||||
|
Figures based on Western European, American and Canadian data. Source: FAO/WHO: Human Vitamin and Mineral Requirements, 2002. |
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| 0-9 years |
200 | 5 | ||||
| 10-18 years |
200 | 5 | ||||
| 19-50 years |
200 | 5 |
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| 51-65 years |
400 | 10 | ||||
| 65+ years |
600 | 15 | ||||
| Pregnancy | 200 | 5 | ||||
| Lactation | 200 | 5 | ||||
Approximate vitamin D levels in foods
| Food | |
μg per serving |
|
IU per serving |
|
% RNI* (for ages 51-65 years) |
||
|
* The RNI (recommended nutrient intake) is defined by the FAO/WHO as “the daily intake which meets the nutrient requirements of almost all (97.5%) apparently healthy individuals in an age- and sex-specific population group”. Daily intake corresponds to the average over a period of time. |
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| Cod liver oil**, 1 tbsp |
23.1 | 924 | 231 | |||||
| Salmon, grilled, 100g |
7.1 | 284 | 71 | |||||
| Mackerel, grilled, 100g |
8.8 |
352 | 88 | |||||
| Tuna, canned in brine, 100g |
3.6 |
144 |
36 | |||||
| Sardines, canned in brine, 100g |
4.6 |
184 |
46 | |||||
| Margarine, fortified, 20g |
1.6 |
62 |
16 | |||||
| Bran Flakes***, average serving, 30g |
1.3 |
52 |
13 | |||||
| Egg, hen, average size, 50g | 0.9 |
36 |
9 | |||||
| Liver, lamb, fried, 100g | 0.9 |
36 |
9 | |||||
