Vitamin D is essential for the development and maintenance of bone, both for its role in assisting calcium absorption from food in the intestine, and for ensuring the correct renewal and mineralization of bone tissue. The type of vitamin D made in the skin is referred to as vitamin D3 (cholecalciferol), whereas the dietary form can be vitamin D3 or a closely related molecule of plant origin known as vitamin D2 (ergocalciferol).
Sources of vitamin D
Vitamin D is made in the skin when it is exposed to ultraviolet B rays; in children and adults exposure of the hands, face and arms to the sun for 10 to 15 minutes per day is usually sufficient for most individuals. However, how much vitamin D is produced from sunlight depends on the time of day, where you live in the world and the color of your skin. Vitamin D can also be obtained from food, and dietary supplements. Food sources are rather limited, and include oily fish such as salmon, sardines and mackerel, eggs, liver, and in some countries fortified foods such as margarine, dairy foods and cereals. Some examples of the approximate vitamin D levels in foods are shown in the table below.
Recommended vitamin D intake
Because the sun provides a source of vitamin D in varying amounts for different individuals, dietary recommendations for vitamin D are approximate. Many countries advise a dietary intake of 200 IU/day (5 µg/day) for children and young adults, and 400-600 IU/day (10-15 µg/day) for older persons, to augment that derived via sun exposure. The Institute of Medicine (IOM) dietary intake recommendations are shown below.
There is as yet no common definition of ‘optimum’ vitamin D status, although there is emerging evidence and expert opinion that the minimum blood level of 25-hydroxyvitamin D that would be optimal for fracture prevention is 70-80 nmol/l1. To achieve this, an average older man or woman would need a vitamin D intake of at least 800-1000 IU/day (20-25 µg/day), which is approximately double the intake recommended in most countries.
For seniors -> Given the indoor-lifestyle of most seniors, little sunshine in winter months, and the various physiological factors related to ageing, it is very common for seniors to have poor vitamin D status. IOF therefore recommends that seniors aged 60 years and over take a supplement at a dose of 800 to 1000 IU/day. Vitamin D supplementation at these levels has been shown to reduce the risk of falls and fractures by about 20%.
Dietary Reference Intakes for Vitamin D
|Age Group||Recommended Dietary Allowance (IU/day)|
|Infants 0-6 months||
|Infants 6-12 months||
Source: Institute of Medicine (IOM), USA
*For infants, Adequate Intake is 400 IU/day for 0-12 months of age
** IOF recommendations for adults aged 60 years and over are 800 to 1000 IU/day for falls and fracture protection
Approximate vitamin D levels in foods
|RNI* (for ages
|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|
* 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.
** Fish liver oils, such as cod and halibut liver oil, contain small amounts of vitamin A, which can be toxic if consumed in excess.
***Bran Flakes are given as an example of a vitamin D-fortified breakfast cereal2.
Factors that interfere with vitamin D synthesis
Dietary or supplemental vitamin D increases in importance during the winter months for populations in northern latitudes, and for elderly people who do not go outdoors much and in whom the capacity for skin synthesis of vitamin D is reduced. Use of sunscreen creams, and a greater degree of skin pigmentation, also reduces the amount of vitamin D that is made in the skin. An increasing body of evidence suggests that on a global level, vitamin D deficiency is widespread, even in very sunny countries such as in the Middle East and parts of Australasia3.
Vitamin D deficiency
In children, severe vitamin D deficiency results in inadequate mineralization of the bone matrix, leading to growth retardation and bone deformities known as rickets. In adults, the same condition is known as osteomalacia. In industrialised countries, rickets and osteomalacia are relatively rare conditions. However, milder degrees of vitamin D inadequacy are common, and can predispose to osteoporosis. Maintaining adequate vitamin D status during pregnancy is important, as there is some evidence that mothers deficient in 25-hydroxyvitamin D in pregnancy give birth to children with reduced bone mass, which could in turn be a risk factor for osteoporosis later in life4. Read more about vitamin D deficiency.
1. Dawson-Hughes B, Heaney RP, Holick MF, et al. (2005) Estimates of optimal vitamin D status. Osteoporos Int 16:713-716
2. Food Standards Agency (2002) McCance and Widdowson’s The Composition of Foods, Sixth summary edition. Cambridge: Royal Society of Chemistry
3. Lim SK, Poor G, Benhamou C-L, et al. (2005) Vitamin D inadequacy is a global problem in osteoporotic women. J Clin Densitom 8 (2):239 (abstract)
4. Harvey NC, Martin R, Javaid MK, et al. (2006) Maternal 25(OH)-vitamin-D status in late pregnancy and MRNA expression of placental calcium transporter predict intrauterine bone mineral accrual in the offspring. Osteoporos Int 17(Suppl. 2):S9 (OC9)
- What is Osteoporosis?
- Who's at Risk?
- Living with Osteoporosis