Balancing the benefits and risks of calcium supplements
Published in Health News and Evidence
Date published: About this date
Calcium supplements are widely used by people with osteoporosis and those at risk of calcium deficiency who are not meeting the recommended dietary intake. Recent reports have outlined an association between calcium supplementation and an increase in cardiovascular events. However, the evidence is currently insufficient to confirm this finding. Further studies and close monitoring is needed to fully understand potential risks of calcium supplementation.
Current clinical practice needs to balance the potential benefits of calcium supplementation on bone health with the potential harms on cardiovascular risk, depending on individual patient factors.
Calcium deficiency leads to a reduction in bone mass by increasing resorption and can contribute to the development of osteoporosis in elderly people.1 As a consequence, fractures are common, especially in women, and are associated with high disability, healthcare costs and mortality.2
To prevent fractures in elderly people, Australian guidelines recommend a diet with sufficient calcium intake.3,4 Calcium supplements are commonly advised for people at risk of calcium deficiency who are not meeting the recommended dietary intakes. Supplements are usually combined with vitamin D, as this promotes calcium absorption. In addition, calcium and vitamin D supplements are commonly recommended for people receiving bisphosphonate treatment for osteoporosis.3,4
In recent years, controversial evidence has emerged about the increased risk of cardiovascular events in people taking calcium supplements.5–7 There is increasing concern that calcium supplements may be doing more harm than good.
Finding the balance of evidence is important to guide decisions on calcium supplementation. However, there is currently insufficient evidence to confidently assess the balance of benefits and harms associated with calcium supplementation.
Calcium supplementation may prevent fractures
Supplementation with calcium and vitamin D has proven benefits for institutionalised elderly women with low dietary calcium intake, significantly reducing risk of hip and non-vertebral fractures.8,9
However, the benefit is less clear for elderly people living in the community. Meta-analysis of randomised controlled trials (RCTs) suggested that calcium supplements reduced the risk of total fractures, but may increase the risk of hip fractures.10,11 Evidence from a large RCT (the Women’s Health Initiative) demonstrated that although calcium with vitamin D supplementation resulted in a small but significant improvement in hip bone density, this did not result in a significant reduction in hip fracture, and increased the risk of kidney stones for healthy postmenopausal women.12
Recommendations for calcium supplementation
The 2009 position statement by the Working Group of the Australian and New Zealand Bone and Mineral Society and Osteoporosis Australia supports the use of calcium and vitamin D supplementation in elderly men and women.3 Their recommendation is based on evidence that supplementation with calcium plus vitamin D prevents fractures in frail elderly people, particularly women in residential care.3 However, this recommendation may need to be reconsidered.
An updated recommendation by the United States Preventive Services Task Force (USPSTF) concludes that there is insufficient evidence to determine if supplementation with calcium and vitamin D affects fracture incidence in men or premenopausal women. It also suggests that supplementation with < 400 IU of vitamin D and 1000 mg of calcium does not prevent fractures. For community-dwelling postmenopausal women it concludes that the evidence is insufficient to determine if supplementation above these levels is effective.13
Calcium and vitamin D supplementation are recommended for patients undergoing treatment for osteoporosis with bisphosphonates, as they are proposed to reduce the rate of bone loss and may reduce fracture rates.4 However, once again evidence from clinical trials is inconsistent.14
Cohort studies have suggested there may be an association between calcium supplementation and increased risk of cardiovascular disease, but data are limited and further trials are unethical in the light of a potentially adverse outcome.
Cardiovascular risks associated with calcium supplementation
Several recent studies have investigated the effect of calcium supplementation on cardiovascular disease. There is a lack of consistency in the findings, making clinical decision making and accurate risk–benefit analysis problematic.
- A systematic review commissioned by the USPSTF on vitamin D supplements with or without calcium concluded that the evidence for calcium supplements and cardiovascular events is inconsistent.9 Among studies that evaluated cardiovascular outcomes, no significant associations were found between calcium intake and cardiovascular events.9
- A reanalysis of the Women’s Health Initiative data demonstrated a significant association between calcium supplements, with or without vitamin D, and higher risk of cardiovascular events in postmenopausal women.15
- A 5-year RCT of calcium monotherapy in 1471 healthy postmenopausal women suggested an association between calcium intake and an upward trend in cardiovascular event rates. However, this was a secondary analysis of data from a study originally designed to investigate the effect of supplementation on bone density. There was only a total of 34 myocardial infarctions over the 5-year study, thus the study was too small to demonstrate a significant difference in such infrequent events.6
- More convincing evidence of a positive association comes from a recent longitudinal study of more than 60,000 elderly Swedish women. This study found that those who had high calcium intake (1400 mg/day) had increased all-cause mortality and incidence of ischaemic heart disease, but not stroke. Mortality was not increased in women with low calcium intake (600–1000 mg/day).7
- A recent meta-analysis reanalysed pooled data from around 12,000 participants involved in 11 RCTs. The results demonstrated a 30% increase in the incidence of myocardial infarction with calcium supplementation (> 500 mg/day) but no significant effect on incidence of other cardiovascular events.5 It is important to note that none of the studies included in this meta-analysis had cardiovascular outcomes as primary endpoints, nor did they randomise their groups based on cardiovascular risk factors.
There is limited evidence from studies investigating dietary calcium to demonstrate an increased risk of cardiovascular events with calcium intake in postmenopausal women.5,6,16 For best clinical practice, ensure adequate daily dietary calcium intake in elderly people to prevent bone loss and fractures. Adequate calcium intake is 1000 mg/day in premenopausal women and 1300 mg/day in postmenopausal women and men older than 70 years.4
- When considering calcium supplementation, assess a patient’s current dietary calcium intake and aim to reach total calcium dose of 1000–1300 mg/day.
- Recommend foods high in calcium that provide protein and other micronutrients that may be important for general health, particularly in frail elderly people.3
- Consider individual patient factors (e.g. gender, age and residential status) before weighing up the potential benefits and risks of calcium supplementation.
- Patients should ensure they have a diet rich in calcium. Recommend foods high in calcium such as dairy products (e.g. milk, cheese and yoghurt), soy or tofu (e.g. calcium-fortified soy milk) leafy green vegetables (e.g. broccoli or spinach), fish, nuts and seeds (e.g. almonds and sesame seed paste).
- To meet the recommended daily guidelines of at least 1000–1300 mg/day patients should consume 3–4 calcium-rich products per day. For example, 200 g of yoghurt or 200 mL of milk provides around 300 mg calcium.
- Recommend adequate vitamin D exposure and consider testing for vitamin D deficiency in people at high risk.
- Recommend regular exercise to all patients as a way to build and maintain healthy bones.
- Zhu K, Prince RL. Calcium and bone. Clin Biochem 2012;45:936–42. [PubMed]
- Rachner TD, Khosla S, Hofbauer LC. Osteoporosis: now and the future. Lancet 2011;377:1276–87. [PubMed]
- Sanders KM, Nowson CA, Kotowicz MA, et al. Calcium and bone health: position statement for the Australian and New Zealand Bone and Mineral Society, Osteoporosis Australia and the Endocrine Society of Australia. Med J Aust 2009;190:316–20. [PubMed]
- Therapeutic Guidelines Limited. Prevention of osteoporosis. 2013. http://etg.hcn.com.au (accessed 1 March 2013).
- Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ 2010;341:c3691. [PubMed]
- Bolland MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ 2008;336:262–6. [PubMed]
- Michaelsson K, Melhus H, Warensjo Lemming E, et al. Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study. BMJ 2013;346:f228. [PubMed]
- 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;327:1637–42. [PubMed]
- Chung M, Balk EM, Brendel M, et al. Vitamin D and calcium: a systematic review of health outcomes. Evid Rep Technol Assess (Full Rep) 2009:1–420. [PubMed]
- Tang BM, Eslick GD, 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. Lancet 2007;370:657–66. [PubMed]
- Reid IR, Bolland MJ, Grey A. Effect of calcium supplementation on hip fractures. Osteoporos Int 2008;19:1119–23. [PubMed]
- Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 2006;354:669–83. [PubMed]
- Moyer VA. Vitamin D and calcium supplementation to prevent fractures in adults: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2013. [Epub ahead of print] [PubMed]
- Christenson ES, Jiang X, Kagan R, et al. Osteoporosis management in post-menopausal women. Minerva Ginecol 2012;64:181–94. [PubMed]
- Bolland MJ, Grey A, Avenell A, et al. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women's Health Initiative limited access dataset and meta-analysis. BMJ 2011;342:d2040.
- Lewis JR, Calver J, Zhu K, et al. Calcium supplementation and the risks of atherosclerotic vascular disease in older women: results of a 5-year RCT and a 4.5-year follow-up. J Bone Miner Res 2011;26:35–41. [PubMed]