Written by Chrystal Moulton, Staff Writer. Overview of the safety of calcium and addresses concerns with over-supplementation of calcium.
Calcium is an essential nutrient required for proper functioning of various systems in the body. It especially plays a very important role in nerve conduction and muscular contraction. (1) Calcium is well-known as the nutrient of choice when taking care of our bones. Much effort over the years has been made to encourage citizens to consume calcium containing products with vitamin D to support bones at an early stage. (2) However, recently, much research has pointed to negative effects of over-supplementation with calcium. Particularly, large epidemiological findings suggest that over-doing calcium supplementation may be linked to a decline in cardiovascular health and death.
Recommended daily intake of calcium is 1000mg in men and women over 19 years old.
Table 1 - Recommended daily intakes of calcium and vitamin D (mg/d)
| Age Range | Calcium | Vitamin D |
|---|---|---|
| Infants 6 to 12 months | 260 mg | 400 IU |
| 1 - 3 years old | 700 mg | 400 IU |
| 19 - 50 years old, pregnant/lactating | 1,000 mg | 600 IU |
| 19 – 50 years old | 1,000 mg | 600 IU |
| 51 – 70 years old | 1,200 mg | 600 IU |
| 71+ years old | 1,200 mg | 800 IU |
Source: NIH Medline Plus(3)
At the recommended allowance, optimal functioning is achieved.(4) Previous research highlights a 12% reduction in the risk of bone fracture with calcium supplementation and the effect was better at 1200mg/d.(1) Higher doses have been administered showing the same results as well. The general population tested were subjects 50 years and over.
Table 2 - Outcomes from previous studies on calcium supplementation| Total subjects | Subject description | Treatment | Duration | Type of study | Results | Adverse events |
|---|---|---|---|---|---|---|
| 2790 (5) | Women in nursing homes(Average age= 84) | 1200mg Ca/ 800IU Vitamin D | 18 months | Randomized, Double-blind, placebo controlled | ↓43% in BF (p<0.05) and ↑2.7% BMD in treatment, ↓4.6% BMD in placebo (p<0.001) | Minor gastric disturbance, hypercalcemia (1 case) |
| 236(6) | Women (postmenopausal)(Average age= 66) | 1600mg Ca | 4 years | Randomized, Double-blind, placebo controlled | ↑0.4% BMD (p = 0.002) at year 1 and ↑0.9% BMD (p = 0.017) at year 4 | Minor gastric disturbance |
| 583(7) | Women (institutionalized, consumed <800mg Ca)(Average age= 85) | 1200mg Ca/800IU Vit. D | 2 years | Randomized, Double-blind, placebo controlled | Hip fracture RR=1.69 (p<0.05) placebo compared to treatment | Minor gastric disturbance, hypercalcimia (3 cases), death rate 18.1% treatment, 23.9% placebo, non-significant ↑urinary Ca in treatment‡ |
| 9605(8) | Men and women(Average age= 74) | 1000mg Ca/800IU Vit. D | 3 years | factorial, cluster-randomized, pragmatic, intervention study | ↓16% fracture incidence rate (p<0.025) | Not mentioned |
| 5292(9) | Men and women(History of fractures)(Average age= 77) | 1000mg Ca/800IU Vit. D | 62 months | factorial, randomized, placebo- controlled | No significant effects | Minor gastric disturbance |
| 1471(10) | Healthy women (postmenopausal)(Average age= 74) | 1000mg Ca | 5 years | Randomized placebo controlled trial | ↓3% in BF, ↓11% in bone turnover, ↑1.5% BMD | Constipation |
| 1460 (11) | Healthy women (postmenopausal)(Average age= 75) | 1200mg Ca | 5 years | Double-blind, placebo controlled | ↓34% BF in subjects with 80% compliance to protocol, otherwise no significant effects | Constipation, 7.7% heart disease in treatment and 7.0% in placebo (ns) |
| 295 (12) | Healthy women (postmenopausal)(Average age= 50) | 1000-2000mg Ca | 2 years | Randomized, Double-blind, placebo controlled | Bone loss (lumbar): ↓1.9% in 1g group, ↓3.0% in 2g group (P<0.001) | Slight increase in serum creatinine levels |
| 36,282 (13) | Healthy women (postmenopausal)(Average age= 62) | 1000mg Ca/400IU Vit. D | 9 years | Randomized, Double-blind, placebo controlled | ↓12% risk of hip fracture (ns), Hip bone density was 1.06% higher in treatment (p<0.01) | ↑incidence of kidney stones in treatment, moderate constipation, (ns) 7.7% incidence of heart disease in treatment, 7% incidence in placebo |
BF: bone fracture; BMD: bone mineral density; ns: not significant
‡Compared to placebo. Urinary Ca >350mg. Baseline was 1.4%, 3.0% at 1yr, and 3.4% at 2yr in treatment. Baseline was 2.3%, 1.3% at 1yr, and 2.9% at 2yr in placebo.
In these clinical studies (in Table 2), the benefits of calcium along with vitamin D supplementation saw benefits in decreasing the incidence of bone fracture, bone resorption, decreasing parathyroid hormone and osteocalcin in serum, and increasing bone mineral density. Most of the studies were done in postmenopausal women since they have a higher rate of osteoporosis.(14) In most of these studies, participants were already consuming calcium from foods in addition to the supplement. In some cases, volunteers were consuming amounts of calcium that were over the recommended daily allowance.(6,12) However, the main side effect evident in these studies was gastric discomfort. Only one study(13) mentioned a non-significant 7% incidence of heart related disease but this occurred in both the treatment and the placebo. Researchers from this study concluded that calcium supplementation posed no risk or benefit to heart disease or cancer.(13)
Nonetheless, many broader epidemiological studies have shown that individuals taking over the recommended daily allowance were more likely to experience a cardiac event. (Table 3) The data demonstrates a general trend yet the evidence in some cases is conflicting. In the AARP Diet study, men consuming 1500mg/d or more of calcium had a higher risk of cardiovascular related death, but in women this association was not seen. In fact, the AARP study shows that between 500-1200mg of total calcium intake, the risk of heart related death decreases in men. (15) There are other studies that demonstrate among post-menopausal women a decrease in stroke and heart disease related to calcium supplementation.(16-18) As an important note, epidemiological studies do not make causal links and thus cannot be used to state any direct relationship between calcium supplements and cardiovascular disease. The evidence seems to demonstrate, nonetheless, that supplementing calcium beyond the recommended daily allowance may not be beneficial to one’s health, but as yet it is still inconclusive.
Table 3 - Studies showing CVD risk with calcium supplementation
| Total subjects | Subject description | Average age (years) | Treatment | Duration | Type of study | Results |
|---|---|---|---|---|---|---|
| 1471 (19) | Healthy post-menopausal women | 74 | 1000mg Ca | 5 years | Randomized, Placebo-controlled | RR heart attack, stroke, or sudden death: 1.21, p=0.043 |
| 388, 229 (15) | Men and women | 50-71 | Not applicable | 12 years | Prospective study, epidemiological | Men: RR for death related to CVD* 1.20, p<0.001Women: RR death related to CVD 1.05, p=0.16 (no risk) |
| 10, 555 (20) | Healthy post-menopausal women | 52-62 | Not applicable | 7 years | Prospective study, epidemiological | hazard ratio (HR) of CHD* 1.24 and CHD morbidity, p<0.05 |
| 23, 980 (21) | Men and women | 35-64 | Not applicable | 11 years | Prospective study, epidemiological | MI* risk for calcium supplement only users HR=2.39 p<0.05 |
CHD=coronary heart disease; CVD=cardiovascular disease; MI=myocardial infarction (heart attack); HR=hazard ratio.
Evidently, more placebo-controlled studies will be needed to determine whether calcium supplementation is directly linked to cardiovascular disease. Until then, 8-10mg/dL of calcium in serum is the key to optimal functioning.(22) Recommended daily intakes of calcium achieve these levels.(4) Chronic diseases and pre-existing conditions may affect absorption of calcium into the bloodstream, therefore, talk with your healthcare provider about steps to take in supplementing calcium.
Posted March 4, 2014.
Chrystal Moulton BA, PMP, is a 2008 graduate of the University of Illinois at Chicago. She graduated with a bachelor’s in psychology with a focus on premedical studies and is a licensed project manager. She currently resides in Indianapolis, IN.
References:
- LarssonSC. Are Calcium Supplements Harmful to Cardiovascular Disease?: Comment on “ Dietary and Supplemental Calcium Intake and Cardiovascular Diseases Mortality: The National Institutes of Health–AARP Diet and Health Study”. JAMA Intern Med. 2013;173(8):647-648.
- Stewart H, Dong D, Carlson A. Why Are Americans Consuming Less Fluid Milk? A Look at Generational Differences in Intake Frequency. Economic Research Report Number 149. United States Department of Agriculture. May 2013. Available at: www.ers.usda. gov/publications/err economic-research-report/ err-149.aspx
- NIH Medline Plus: New recommended daily amounts of calcium and vitamin D. http://www.nlm.nih.gov/medlineplus/magazine/issues/winter11/articles/winter11pg12.html. Accessed February 27, 2014.
- ” 5 Dietary Reference Intakes for Adequacy: Calcium and Vitamin D .” Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press, 2011.
- MC Chapuy, ME Arlot, F Duboeuf et al. Vitamin D3 and calcium to prevent hip fractures in the elderly women. N Engl J Med, 327 (1992), pp. 1637–1642
- B Riggs, et al. Long-term effects of calcium supplementation on serum parathyroid hormone level, bone turnover, and bone loss in elderly women. J Bone Miner Res, 13 (1998), pp. 168–174
- M Chapuy, R Pamphile, E Paris et al. Combined calcium and vitamin D3 supplementation in elderly women: confirmation of reversal of secondary hyperparathyroidism and hip fracture risk: the Decalyos II study. Osteoporos Int, 13 (2002), pp. 257–264
- E Larsen, L Mosekilde, A Foldspang. Vitamin D and calcium supplementation prevents osteoporotic fractures in elderly community dwelling residents: a pragmatic population-based 3-year intervention study. J Bone Miner Res, 19 (2004), pp. 370–378
- The RECORD Trial Group: 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. Lancet, 365 (2005), pp. 1621–1628
- I Reid, B Mason, A Horne et al. Randomized controlled trial of calcium in healthy older women. Am J Med, 119 (2006), pp. 777–785
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- P Elders, J Netelenbos, P Lips et al. Calcium supplementation reduces vertebral bone loss in perimenopausal women: a controlled trial in 248 women between 46 and 55 years of age. J Clin Endocrinol Metab, 73 (1991), pp. 533–540
- RD Jackson, AZ LaCroix, M Gass et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med, 354 (2006), pp. 669–683
- Osteoporosis and bone health. AAOS Now. May 2009 Issue. Accessed March 3, 2014. available at: http://www.aaos.org/news/aaosnow/may09/clinical8.asp
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- Iso H, Stampfer MJ, Manson JE, et al. Prospective study of calcium, potassium, and magnesium intake and risk of stroke in women. Stroke1999;30:1772-9.
- Knox EG. Ischaemic-heart-disease mortality and dietary intake of calcium. Lancet1973;ii:1465-7.
- Bolland MJ, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ. 2008 ;336(7638):262-6.
- Pentti K, Tuppurainen MT, Honkanen R, et al. Use of calcium supplements and the risk of coronary heart disease in 52-62-year-old women: the Kuopio Osteoporosis Risk Factor and Prevention Study. Maturitas. 2009;63(1):73-78
- Li K, Kaaks R, Linseisen J, Rohrmann S. Associations of dietary calcium intake and calcium supplementation with myocardial infarction and stroke risk and overall cardiovascular mortality in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study (EPIC-Heidelberg). Heart. 2012;98(12):920-925
- Calcium – blood test. Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/003477.htm. Accessed March 3, 2014.
