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Back to Vitamin D

Vitamin D and Bone Health

It is well known that vitamin D influences the development and maintenance of bone mass and reduces the risk of osteoporosis. Furthermore, it is also thought to improve lower limb neuromuscular function.

Highlights

  • A cause-and-effect relationship has been established between intakes of
    vitamin D from food and supplements and the growth, development and maintenance of bones and teeth, lower limb neuromuscular function and a reduced risk of osteoporotic fractures;
  • Serum 25(OH)D concentration may be positively associated with bone mineral density in children over the age of 6 months, adolescents, and adults (both younger and older) of different ethnic origins;
  • The beneficial effects of vitamin D on bone health are recognized by different health authorities, including Health Canada, the U.S. Food and Drug Administration, the Institute of Medicine and the European Food Safety Authority;
  • There are differing opinions regarding the dose of vitamin D and the desirable serum 25(OH)D concentrations required for optimal bone health outcomes.

Introduction

Vitamin D from food, supplements and sun exposure is first transformed in the liver into 25‑hydroxyvitamin D [25(OH)D] and is then activated in the kidneys as 1,25-dihydroxyvitamin D or calcitriol.1 This hormonally active form is responsible for the homeostasis of calcium and phosphorus, whereas serum 25(OH)D concentrations reflect vitamin D status.2 Serum 25(OH)D concentrations and intakes of vitamin D (from both food and supplements) may be significantly and positively associated with bone mineral density (BMD).1,3

Aging leads to a loss of bone mass and decreased vitamin D synthesis, which may contribute to the development of osteoporosis. Inadequate intake of calcium and vitamin D may aggravate the situation and increase the risk in particular of vertebral, hip and forearm fractures.1 Osteoporosis is more common in women than men4 due to decreased concentrations of estrogen at menopause, which promote a reduction in BMD.

The beneficial effects of vitamin D on the absorption and use of calcium and phosphorus, its contribution to the development of solid bones, and its ability to reduce the risk of osteoporosis are recognized by different health authorities, including Health Canada, the U.S. Food and Drug Administration (FDA), the Institute of Medicine (IOM) and the European Food Safety Authority (EFSA).1 According to these agencies, data support the conclusion that there is an independent cause-and-effect relationship between calcium and vitamin D intakes and the growth, development and maintenance of bones and teeth, and a reduced risk of osteoporotic fracture.

The Evidence

After conducting a comprehensive review of the evidence to date, the IOM found data suggesting that there is a dose-dependent association between 25(OH)D concentrations and bone mineral content in children over the age of 6 months, adolescents, and adults (both younger and older) of different ethnic origins.1 A vitamin D serum concentration of 50 nmol/L was deemed to be sufficient to ensure bone health outcomes.1

Data have also demonstrated that treatment combining a vitamin D supplement and a calcium supplement may also reduce bone loss and may lead to a greater increase in BMD compared to treatment without vitamin D.5 Vitamin D may also improve lower limb neuromuscular function and decrease the frequency of falls.5

The results of a 2010 meta-analysis of 8 studies indicate that combined vitamin D and calcium supplementation can decrease the incidence of nonvertebral fractures by 23% and hip fractures by 30%.6

  • This supplementation may also reduce fractures other than hip fractures to a greater degree compared to calcium supplementation alone;
  • Fractures of the hip and vertebrae seem to be more frequent among older people with deficient intakes of vitamin D and calcium, whereas other fractures are more common among people who are older but who are active and who have higher intakes of these two nutrients.

A 2009 meta-analysis of 20 randomized controlled trials on fractures in people over the age of 65 showed that vitamin D supplementation of more than 482 IU per day reduced nonvertebral fractures by 20% and hip fractures by 18%.7

  • The reduction in nonvertebral fractures was greater when higher doses of vitamin D were used;
  • In terms of supplementation with doses below 400 IU, no decrease in hip fractures was observed;
  • The addition of calcium to the vitamin D supplementation did not influence the reduction of nonvertebral fractures;
  • Cholecalciferol (D3) seems to be more effective than ergocalciferol (D2) at decreasing fractures, as, at an equivalent dose, it seems to increase 25(OH)D levels to a greater degree because of greater vitamin D receptor affinity.

Another meta-analysis of randomized controlled trials indicated that vitamin D supplementation in people at risk of hip fractures (postmenopausal women or men aged 50 years and over) reduced the risk of hip fractures by 18% only when the supplement was combined with calcium.8

Similarly, a meta-analysis of 45 studies revealed that combined supplementation with 400 to 800 IU of vitamin D and 1,000 mg of calcium per day reduced the incidence of hip fractures by 16%.9 However, this effect may be greater for individuals whose daily intakes of vitamin D are below 400 IU. Furthermore, vitamin D supplements alone and those that combined both vitamin D and calcium were less effective at preventing fractures than calcium supplements alone.9

Potential Mechanisms

Vitamin D regulates blood calcium levels by improving the intestinal absorption of calcium and minimizing its elimination in the urine. It also plays a role in the deposit of calcium in bone and the removal of calcium from bone to meet the body's needs.1 A vitamin D deficiency results in a low absorption of calcium and elevated concentrations of parathyroid hormone (PTH), a hormone that acts to increase blood calcium levels by releasing calcium from the bones.10

Over the long term, vitamin D deficiency leads to a loss of bone mass, which weakens the bones and causes osteoporosis. Adequate vitamin D intake decreases bone loss by reducing the secretion of PTH and prevents excessive bone remodelling (bone turnover). Several data show that high bone remodelling rates increase bone fragility.1 Furthermore, this rate doubles across menopause and triples by the age of 65 years.

Conclusions

Vitamin D plays a role in helping people reach and maintain adequate BMD. Some populations, such as children who present with a vitamin D deficiency and seniors living in long-term care facilities, would benefit more from vitamin D supplementation. The dose of vitamin D required to reduce the incidence of fractures is controversial. In studies that showed evidence of decreased fractures in seniors, a minimum dose of 400 IU of vitamin D was required.

To ensure the maintenance of bone health, the IOM recommends a serum 25(OH)D concentration of 50 nmol/L. However, some experts suggest that concentrations should be above 75 nmol/L.1,11 These concentrations would limit bone resorption and demineralization by preventing an increase in PTH levels. As a preventive measure, Health Canada recommends that all adults over the age of 50 years take a daily vitamin D supplement of 400 IU.1 However, Osteoporosis Canada suggests that adults under the age of 50 years take a supplement of 400 to 1,000 IU per day and that people over the age of 50 years or younger adults at higher risk of osteoporosis take a supplement of 800 to 2,000 IU per day.14

References

  1. Institute of Medicine. Dietary Reference Intakes for calcium and vitamin D. Washington, DC: The National Academies Press, 2011.
  2. Gropper SS and Smith JL. Advanced nutrition and human metabolism. Washington DC: Cengage Learning, 2009.
  3. Nakamura K and Iki M. Efficacy of optimization of vitamin D in preventing osteoporosis and osteoporotic fractures: a systematic review. Environ Health Prev Med 2006;11(4):155-70.
  4. Becker C. Pathophysiology and clinical manifestations of osteoporosis. Clin Cornerstone 2006;8(1):19-27.
  5. Lips P and van Schoor NM. The effect of vitamin D on bone and osteoporosis. Best Pract Res Clin Endocrinol Metab 2011;25(4):585-91.
  6. Bergman GJ et al. Efficacy of vitamin D3 supplementation in preventing fractures in elderly women: a meta-analysis. Curr Med Res Opin 2010;26(5):1193-201.
  7. Bischoff-Ferrari HA et al. Prevention of nonvertebral fractures with oral vitamin D and dose dependency: a meta-analysis of randomized controlled trials. Arch Intern Med 2009;169(6):551-61.
  8. Boonen S et al. Need for additional calcium to reduce the risk of hip fracture with vitamin D supplementation: evidence from a comparative meta-analysis of randomized controlled trials. J Clin Endocrinol Metab 2007;92(4):1415-23.
  9. Avenell A et al. Vitamin D and vitamin D analogues for preventing fractures associated with involutional and post-menopausal osteoporosis. Cochrane Database Syst Rev 2009;(2):CD000227.
  10. Heaney RP. Bone health . Am J Clin Nutr 2007;85(1):300S-303S.
  11. Dawson-Hughes B et al. Estimates of optimal vitamin D status. Osteoporos Int 2005;16(7):713-6.
  12. Souberbielle JC et al. Vitamin D and musculoskeletal health, cardiovascular disease, autoimmunity and cancer: recommendations for clinical practice. Autoimmun Rev 2010; 9(11):709-15.
  13. Grant WB et al. An estimate of the economic burden and premature deaths due to vitamin D deficiency in Canada. Mo Nutr Food Res 2010;54(8):1172-81.
  14. Osteoporosis Canada. La vitamine D : un élément clé pour une bonne absorption du calcium. Consulted February 25, 2013.

Keywords: fractures , vitamin D , osteoporosis


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