Osteoporosis and the role of calcium and vitamin D

Expert opinion, July 2010

Kelly Shaw

Dr Kelly Shaw

 


Osteoporosis is a disease characterised by low bone mass and deterioration of bone tissue, leading to increased bone fragility and a consequent increase in fracture risk. It is diagnosed by a bone density test that usually measures the density at the hip and spine. The result is called a 'T-score', and will be in the range of normal, osteopaenia ('fragile' bones but not 'fragile' enough to be classified as osteoporosis), or osteoporosis.

Osteoporotic fractures usually result from a combination of decreased bone strength and injury, commonly falls. They are generally classified as vertebral (spinal) or non-vertebral:

  • Vertebral fractures are less common than non-vertebral fractures. However, when they do occur, their cause is usually osteoporosis. About a third of vertebral fractures are associated with falls and most are precipitated by routine activities such as bending or lifting.
  • Non-vertebral fractures at these non-vertebral sites, including hip, distal forearm, humerus, shoulder, ankle, pelvis and tibia, are approximately twice as common in women as in men

How common is osteoporosis?

According to the World Health Organization definition of osteoporosis approximately 11% of men and 27% of women aged 60 years or over have osteoporosis.

Osteoporotic fractures occur more frequently among women than men and increase with age in both genders. The lifetime risk of minimal trauma fracture is approximately 43% for women over 50 years of age and 56% among women over 60 years of age. The lifetime fracture risk among men is lower, but still substantial and higher than for many other chronic conditions - 27% for those over 50 years of age and 29% for men over 60 years of age.

Osteoporosis treatment

Osteoporosis is treated with a combination of drug treatment, vitamin/mineral supplementation and lifestyle advice.

Drug treatment is indicated to prevent further bone loss and reduce subsequent fracture risk in people with osteoporosis. Treatment decisions are based on age, gender, previous medical history, how advanced the condition is and an estimate of absolute risk of fracture. Despite the effectiveness of drug treatment, less than 30% of women and even fewer men with osteoporosis take specific osteoporosis targeted pharmaceuticals.

Calcium and vitamin D are the mainstay of vitamin/mineral supplementation for osteoporosis treatment. Calcium and vitamin D work by reducing secondary hyperparathyroidism and reducing bone turnover. Bone mineral density is also increased by calcium and vitamin D, but their effects appear to be modest. Their role in osteoporosis treatment is discussed in detail below.

Advice also needs to be provided to assist the individual address their modifiable risk factors, as part of the treatment of osteoporosis. This routine health care approach includes encouragement and support to increase weight bearing physical activity, to maintain a healthy diet and to avoid smoking and excessive alcohol intake. Exercise can assist in relieving pain as part of the rehabilitation process.

The role of calcium and vitamin D in osteoporosis treatment

Calcium intake is often suboptimal in the elderly (especially institutionalised patients) who may have limitations to dietary intake and relatively limited sunlight exposure. Calcium supplementation is commonly required in this patient group. There is also good evidence for high prevalence of vitamin D insufficiency in institutionalised and home bound individuals and vitamin D supplementation is considered to be standard care in these populations.

Most specific anti-osteoporosis drug therapies were evaluated in the context of adequate vitamin D stores and adequate calcium intake. Appropriate supplementation with calcium and/or vitamin D is recommended in patients starting drug therapy if calcium intake and/or vitamin D levels are inadequate.

An international guideline based on three good quality systematic reviews reported that dietary calcium is as effective as supplements for adequate calcium balance. According to published studies, 1000 mg dietary calcium daily is associated with a 24% lower rate of hip fractures.

The main sources of dietary calcium are dairy milk, cheese (not soft) and yoghurt. Other foods that provide a moderate source of dietary calcium include white bread, sardines and calcium enriched soy milk. Patients who cannot achieve an adequate calcium intake through diet alone may require additional supplementation.

Vitamin D also has an important role in maintaining bones by promoting the absorption of calcium. Although some vitamin D is found in the diet (e.g. fatty fish) the primary source is from exposure to sunlight. The amount of sunlight required to produce optimum levels of vitamin D varies between guidelines, and according to ethnicity. Exposure of approximately 15% of the body (i.e. hands, face and arms) for 6–8 minutes, 4–6 times per week, and before 10 am or after 2 pm (standard time) for moderately fair skinned people is generally supported. Darker skinned ethnic groups require greater daily sunlight exposure.

According to published guidelines, total calcium intake from dietary sources and supplements should exceed 1200 mg/day. Vitamin D from sunlight exposure (avoiding the middle of the day) and supplements should ensure 25-hydroxyvitamin D (25-OH D) levels >60 nmol/l. If vitamin D supplements are required, doses of at least 800 IU/day are usually required.

Calcium supplements are available in two common forms: calcium carbonate and calcium citrate. The most commonly available type of vitamin D supplement is vitamin D3 or cholecalciferol. It elevates serum 25-OH D concentrations more than vitamin D2 or ergocalciferol, and is also more reliably measured by commercially available assays. Currently available doses range from 400–1000 IU, presented as either capsules or tablets.

Calcium supplements can uncommonly increase the risk of renal calculi, particularly if given to individuals with adequate dietary calcium intakes. Calcium supplements can cause abdominal bloating and constipation. One RCT75 reported an increase in cardiovascular adverse events with calcium in older postmenopausal women, however further research is required.

Toxicity is extremely uncommon with vitamin D.

The role of calcium and vitamin D in osteoporosis prevention

Calcium and vitamin D also play an important role in the prevention of osteoporosis. Suboptimal calcium intake and vitamin D deficiency are important public health problems and increase the risk of fractures, particularly in women and men aged 70 years over. Vitamin D deficiency is associated with a higher risk of falling as well as with a lower bone density.

There is mixed evidence on the effectiveness of calcium and vitamin D supplementation for prevention of bone loss and osteoporotic fractures in postmenopausal women and older men. There may be some benefit for those who have inadequate levels, particularly institutionalised patients.

Total calcium intake from dietary sources and supplements should exceed 1200 mg/day. Vitamin D from sunlight exposure (avoiding the middle of the day) and supplements should ensure 25-hydroxyvitamin D (25-OH D) levels >60 nmol/l. If vitamin D supplements are required, doses of at least 800 IU/day are usually required.

Health care providers could recommend sensible, moderate levels of physical activity throughout life as part of a healthy lifestyle and for osteoporosis prevention. However, no studies have demonstrated any efficacy in fracture risk reduction and addressed side effects such as injuries.

References

  • Adami S, Giannini S, Bianchi G, et al. Vitamin D status and response to treatment in post-menopausal osteoporosis. Osteoporosis International 2009;20(2):239–44.
  • Avenell A, Gillespie W, Gillespie L, et al. Vitamin D and vitamin D analogues for preventing fractures associated with involutional and post-menopausal osteoporosis. Cochrane Database of Systematic Reviews 2006; Issue 4:Art. No.: CD000227. DOI: 10.1002/14651858.CD000227.pub2.
  • Bischoff-Ferrari H, Dawson-Hughes B, Baron J, et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomised controlled trials. American Journal of Clinical Nutrition 2007;86(6):1780–90.
  • Boonen S, Lips P, Bouillon R, et al. Need for additional calcium to reduce the risk of hip fracture with vitamin D supplementation: evidence from a comparative meta-analysis of randomised controlled trials. Journal of Clinical Endocrinology and Metabolism 2007;92(4):1415–23.
  • Cooper C, Melton L. Vertebral fractures, how large is the silent epidemic? British Medical Journal 1992;304:793–94.
  • Grant A, Avenell A, Campbell M, et al. Oral vitamin D3 and calcium for secondary prevention of low-trauma fractures in elderly people (Randomised Evaluation of Calcium Or vitamin D, RECORD): a randomised placebo-controlled trial. The Lancet 2005;365(9471):1621–28.
  • NHMRC / RACGP. 2010. Clinical guideline for the prevention and treatment of osteoporosis in postmenopausal women and older men.
  • Osteoporosis Australia. Osteoporosis – diagnosis. 2007 [updated 2007; cited 2009 Jan]. Available at www.osteoporosis.org.au/osteo_diagnosis.php.
  • Pfeilschifter J. 2006 DVO-guideline for prevention, diagnosis, and therapy of osteoporosis for women after menopause, for men after age 60 executive summary guidelines. Experimental and Clinical Endocrinology and Diabetes 2006;114(10):611–20.
  • Tang B, Eslick G, Nowson C, et al. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. The Lancet 2007;370(9588):632–34.
  • World Health Organization. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis: Report of a WHO Study Group. Geneva: WHO, 1994 (Technical Report Series 843). Journal of the American Medical Association 2001;285:785–95.
  • Woolf A, Pfleger B. Burden of major musculoskeletal conditions. Bulletin of the World Health Organization 2003;81(9):646–56.