It is well known that calcium is essential for bone health, and that inadequate intakes of calcium can lead to osteoporosis. However, many people don’t realize that Vitamin D is needed for the absorption of calcium. In fact, without vitamin D, calcium passes through the intestines unabsorbed, leaving the bone undersupplied even when calcium intakes are adequate.1 Vitamin D also helps to transport calcium into the bone, which enhances bone mineralization, and it stimulates the retention of calcium by the kidneys making more calcium available for the bones. In addition to aiding with bone mineral density, vitamin D has been found to improve balance in the elderly, which can help reduce the risk of falls. Although studies have not all been consistent in showing this, it could prove to be another example of how vitamin D can reduce the risk of fractures.2,3
There are two forms of Vitamin D that are important to humans, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is derived from plant sources but its contribution in the diet is minor. Vitamin D3 is derived from animals and is found naturally in egg yolks, liver, fatty fish and butter. Since these are primarily the only foods that naturally contain vitamin D, some foods are fortified with the nutrient such as milk. Humans can also synthesize vitamin D3 from the diet or when skin is exposed to ultraviolet-B rays from sunlight.
So how much Vitamin D is needed? Depending on age, the amount of Vitamin D needed by the body varies. (Vitamin D is most commonly expressed in international units (IU) but is sometimes seen in micrograms (mcg)). The recommendations are as follows:
- 1-50 years: 200 IU (5mcg) or approximately 2 cups of Vitamin D fortified Milk.
- 51-70 years: 400 IU (10mcg) approximately 4 cups of Vitamin D fortified Milk.
- 71 years and older: 600 IU (15mcg) approximately 6 cups of Vitamin D fortified Milk.
However, there has been debate as to whether the current recommendations should be increased due to growing evidence indicating that they may not be adequate to meet nutrition needs or support bone health. This topic has recently received a lot of attention due to a significant rise in the number of people who have been diagnosed with vitamin D deficiencies. When the Dietary Reference Intakes (DRIs) were set, it was presumed that the average adult gets the majority of their vitamin D from sunlight exposure with the diet contributing a small amount of this nutrient. Vitamin D deficiencies have been found to occur in people with limited sun exposure; particularly those who live in northern latitudes, smoggy cities or those who are housebound.
In order to get adequate vitamin D from the sun, it only takes about 10-15 minutes of exposure to the hands, face and arms a few times a week for most people. However, those with a darker pigment may require longer exposure to the sun, and the use of sunscreen with an SPF of 8 or greater prevents vitamin D synthesis.
For those who are shielded from the sunlight, a vitamin D supplement should be considered because it is very difficult to get adequate amounts of vitamin D in the diet alone. The average person is estimated to only consume about 150 IU from food sources. When choosing a supplement, Vitamin D3 is the preferable source because it is more stable and 3.4 times more potent than vitamin D2. As demonstrated in several studies, approximately 800 IU/day has been the dosage shown to help maintain bone density and reduce the risk of fractures in the elderly.4,5 Supplementing the diet with both calcium and vitamin D has been found to be more effective at preventing fractures than calcium or vitamin D supplements alone.6 It is important to note that people with hyperparathyroidism, sarcoidosis and those on calcium-channel blockers or thiazide diuretics should talk with their doctor before starting a vitamin D supplement.
Upper limits (ULs) have been set at 2,000 IU/day (50mcg) for adults, but some feel that the safe ULs may be as high as 4,000-10,000 IU/day. Too much vitamin D can cause herpercalcemia, bone loss, kidney stones and calcification of soft tissues and the kidneys, but this is rarely seen in less than 40,000IU/day,7 and sunlight can not cause toxicities. However, until more research is available to determine the safety of higher doses, it would be prudent to limit intakes to intakes to a maximum 2,000 IU/day.
1. Whitney EN, Rolfes SR. Understanding nutrition: seventh edition.
2. Flicker L, MacInnis RJ, Stein MS, et al. Should older people in residential care receive vitamin D to prevent falls? Results of randomized trial. J Am Geriatr Soc. 2006;54:1020-1021.
3. Bischoff-Ferrari HA, Dawson-Hughes BD, Willett WC, et al. Effect of vitamin D on Falls: a meta-analysis. JAMA. 2004; 291:1999-2006.
4. Chapuy MC, Arlot ME, Duboeuf F, et al. Vitamin D3 and calcium to prevent hip fractures in the elderly women. N Engl J Med. 1992;327:1637-1642.
5. Vischoff-Ferrari HA, Willett WC, Wong JB, et al. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. JAMA. 2005;293:2257-2264.
6. Meyer HE, Smedshaung GB, Kvaavik E, et al. Can vitamin D supplementation reduce the risk of fracture in the elderly? A randomized controlled trial. J Bone Miner Res. 2002;17:709-715.
7. Parfitt AM, Gallagher JC, Heaney RP, et al. Vitamin D and bone health in the elderly. Am J Clin Nutr. 1982;36:1014-1031.