Introduction
The premise that calcium consumption makes bones stronger must be qualified by age. It is well established that bone formation, up to 35 years of age, is the prominent activity in bone. During this time, strong bone formation depends on adequate calcium intake and stress/strain on bone (i.e. physical activity). Strong bones resist fractures and thereby allow for unlimited mobility and independence.
However, in the older adult (after age 35), bone formation ceases and is replaced by remodeling, a type of repair of microdamage. Calcium may relocate in bone but chronic accumulation of additional calcium driven by calcium consumption does not occur. Therefore, as this blog will discuss, neither dietary nor supplemental calcium puts calcium back into bones of older adults and furthermore, neither has an effect on reducing the risk of fractures. In particular, several adverse effects are associated with use of calcium supplements.
Bone biology
The bones of our skeletal system serve many important functions. Bones support our muscles for balance, provide form and allow mobility. Bones protect our internal organs (lungs, heart, brain), and act as the largest reservoir for the essential mineral, calcium.
Importance of calcium
The body requires calcium for just about every function in the body. This includes the contraction of our muscles, nerve conduction and release of neurotransmitters, enzyme activity for metabolism, and secretion of hormones and bioactive factors, to name a few.
Two hormones, the parathyroid hormone and calcitonin, assure that blood calcium is tightly controlled within a narrow range so that these functions are adequately maintained. Although rare, blood calcium levels that are too high or too low produce adverse effects. For example, chronic high levels of calcium produce kidney stones and chronic low levels of calcium produce thin weak bones.
Bone Formation in the Young Adult
The optimal time to increase bone density is during growth up to 35 years of age. Thus, the greater the bone density at age 35, the less likely the occurrence of a fracture as one ages, even in the presence of unavoidable menopausal-driven bone calcium loss. Assuming a normal diet with adequate calcium intake, achieving high bone density throughout one’s growth by participating in sports, work-outs, and/or physically demanding activities, is the only way to prevent osteoporosis in later life.
A diagnosis of osteoporosis is given when density of bone minerals i.e. calcium reaches a predetermined value (in comparison to the average bone density of a 30 year old). This chosen low density value is significant because it indicates an elevated risk of a fracture. Osteoporosis is managed with one of several prescription drugs that act to strengthen bones.
Bone Loss in the Older Adult
Bone mineral density declines with age in both women and men due to key factors such as hormonal changes, loss of muscle mass and reduced level of physical activity. However, the impact on older women is especially acute due to 1) the lower level of bone mineral density achieved early in life (smaller muscle mass and reduced participation in sports) and 2) the severe reduction of estrogen with menopause.
Estrogen is the premier driver of bone formation. Estrogen production largely ceases in menopause (around 50-55 years) and is slightly reduced in older males. This change results in a significant decline in bone maintenance and remodeling leading to subsequent loss of bone minerals. Bones become less dense and less strong with an elevated potential for fractures on minimal impact.
Benefit/risk assessment of calcium supplements and risk of fractures
The daily use of calcium supplements with or without added vitamin D is widespread among middle-aged and postmenopausal women. This activity supported a 3.8 billion dollar industry in 2022 with a projected doubling in 2023 (https://www.futuremarketinsights.com/reports/calcium-supplements-market).
Beginning in the 1980s, with very little human data, the medical and pharmaceutical industry promoted consumption of calcium supplements for optimal bone health. Whereas the calcium-deficient individual benefitted from calcium plus vitamin D supplements in the treatment of serious bone loss diseases (osteoporosis, osteomalacia) with its high risk of fractures, individuals without calcium deficiency and no bone disease were similarly assumed to benefit from calcium supplements that were purported to create stronger bones, and hence fewer fractures. The data from many randomized clinical trials do not support this.
Calcium supplements do not prevent fractures
The loss of bone calcium with age prompted the use of calcium supplements with and without vitamin D to reverse this. Sadly, this does not work. The few studies that measured bone density during use of calcium supplements found only transient small increases in bone density that were not preserved over time (1). In other words, there was no consistent and persistent increase in bone density. Most importantly, the result of numerous randomized clinical trials concluded that the use of calcium supplements has no effect on the main endpoint, prevention of fractures.
Meta-analysis
To assess the massive literature on the relation of calcium supplements to fracture risk, the meta-analysis approach selects and critiques the best (low bias) randomized clinical trials. Among all studies relating to calcium supplements and fractures, those selected for the meta-analysis meet rigorous criteria such as randomization, placebo control, duration greater than 1 year, adults over 50 years, and specific validated endpoint e.g. evidence of a fracture. The results of 6 meta-analyses (2-7) each analyzing 10-20 trials concluded that consumption of calcium with or without vitamin D did not change the risk for fractures (hip, vertebral, non vertebral) in community-dwelling older adults. The one exception, noted in one study (8), calcium supplements benefit frail institutionalized older adults with osteoporosis.
Calcium supplements exert adverse effects
1. Cardiovascular risk
There has been a long standing concern that calcium supplements may adversely affect the heart and blood vessels. In support of this concern are the results from a major “study assessing the association of calcium intake, source of calcium intake, and coronary artery calcification in a large, multiethnic sample of US men and women at both baseline and with repeat longitudinal estimates of incident coronary artery calcification up to 10 years” (9). Importantly, coronary artery calcification was associated with calcium supplement intake but not with dietary calcium intake. Coronary artery calcification is a biomarker of cardiovascular risk because calcium locates to artery plaques. Hence, its presence may contribute to plaque formation and increase the risk for heart disease.
1a. Important clinical trials
There have been numerous clinical trials examining the relation of calcium supplements to risk of cardiovascular disease, clinically as defined by a heart attack, stroke or cardiovascular death. Using meta-analysis, it is concluded that use of calcium supplements increases the risk of cardiovascular disease (10-12). In contrast, unlike calcium supplements, one meta-analysis reported that dietary calcium did not increase the risk of cardiovascular disease (10).
An additional study of note because of its long duration of 20 year is a prospective cohort study (13). This study concluded that calcium supplements do not increase the risk for cardiovascular disease. However, unlike a randomized clinical trial in which randomization and placebo controls are required to reduce bias, the prospective cohort study tracks individuals over a long period, taking measurements throughout but without randomization or controls.
2. Kidney stones and GI issues
Although not as well investigated as adverse cardiovascular effects, gastrointestinal effects, in particular constipation is associated with intake of calcium supplements. It is generally considered a minor issue but in fact, it is the main reason for lack of compliance in clinical trials with calcium supplements (14).
Additionally, use of calcium supplements increases urinary calcium (15) which has the potential to cause kidney stones. Inadequate fluid intake elevates the risk of kidney stones with calcium supplements (16).
Dietary Calcium and Fractures
Meta-analysis of clinical trials show that dietary calcium intake can fluctuate significantly and still have no effect on risk of fracture. A relevant example is the Auckland Calcium Study which followed 500 postmenopausal women (not taking hormone replacement therapy or calcium supplements) and measuring bone density numerous times over a 5 year period. Dietary calcium ranging from 400-1500 mg/day had no effect on the number of fractures (1). Anderson et al., 2016 cited above, reported that while calcium supplement intake is associated with coronary artery calcification, dietary calcium intake is not. Dietary calcium also is not associated with adverse effects evident with calcium supplements (10).
RDA and Fractures
It is clear that ingesting calcium by diet or by supplements does little to fortify the bones in older adults. So why bother about even dietary calcium consumption? The answer is that dietary calcium is essential for a vast variety of physiological activities such as muscle contraction and nerve activity (see Importance of Calcium section). Thus the need for a recommended daily allowance (RDA). If the RDA is not met, then the body will “steal” calcium from the best depot, bone.
The Food and Nutrition Board sets the RDA (https://www.nationalacademies.org/fnb/food-and-nutrition-board). For women over 50 years of age, the calcium RDA is 1200/day. For men 51-70 years of age, it is 1000 mg/day and 1200 mg/day for men over 70 years of age. Interestingly, calcium RDA is based on results of calcium balance studies which determines the amount of calcium consumed that counterbalances the amount excreted in the urine, GI tract and skin. Balance studies are technically challenging so estimates are the norm. Neither bone density nor fracture risk were assessed in determining the calcium RDA. Therefore, calcium RDA is independent of bone calcium density and fracture risk. It merely determines the amount needed to keep blood calcium constant so that all calcium-dependent activities can continue.
Fall prevent might help reduce fractures
Since dietary and supplemental calcium do not reduce fracture risk, what strategies might diminish risk? Many fractures result from falls. Fortunately, fall prevention is achievable. Activities/strategies that work include 1) balance and resistance exercises to increase body stability and muscle strength (see Blog 2, 3, 5), 2) environmental changes – decrease house clutter, proper lighting, remove area rugs, 3) assure good eyesight and hearing, 4) reduce polypharmacy (use of 4 or more drugs) (see Blog 21) and 5) avoid multitasking when walking.
Conclusions
It is apparent, certainly in community-dwelling older adults, that calcium supplements have no real benefit on bone density or reduction of fracture risk. Calcium supplements offer only the potential for adverse effects. Dietary calcium intake also is independent of fracture risk but unlike supplements does not exert adverse events. Although calcium from a normal healthy diet such as the Mediterranean diet (see Blog 11) will not fortify or compensate for bone loss, it will contribute to an adequate blood calcium level required for maintenance of essential body functions.
References
1. Reid IR et al., Calcium supplements: benefits and risks. Journal of Internal Medicine. 2015, 278: 354–368.
2. Jackson RD et al., Calcium plus Vitamin D Supplementation and the Risk of Fractures. N Engl J Med. 2006; 354: 669-83.
3. Bollard MJ et al., Calcium intake and risk of fracture: systematic review. BMJ. 2015; 351: h4580.
4. Harvey NC et al., The role of calcium supplementation in healthy musculoskeletal ageing: An Experts consensus meeting of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) and the International Foundation for Osteoporosis (IOF). Osteoporosis Int. 2017 February; 28(2): 447–462.
5. Zhao JG et al., Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis. JAMA. 2017 Dec 26; 318(24): 2466–2482.
6. Hu ZC et al., Comparison of fracture risk using different supplemental doses of vitamin D, calcium or their combination: a network meta-analysis of randomized controlled trials. BMJ Open.2019;9:e024595.
7. Karti K et al., Role of calcium &/or vitamin D supplementation in preventing osteoporotic fracture in the elderly: A systematic review & meta-analysis. Indian J Med Res. 158: 5-16, 2023.
8. Chapuy MC et al., Vitamin-D3 and calcium to prevent hip fractures in elderly women. N Engl J Med. 1992; 327: 1637–42.
9. Anderson JJB et al., Calcium Intake From Diet and Supplements and the Risk of Coronary Artery Calcification and its Progression Among Older Adults: 10-Year Follow-up of the Multi-Ethnic Study of Atherosclerosis (MESA) J Am Heart Assoc. 2016;5:e003815.
10. Yang C et al., The evidence and controversy between dietary calcium intake and calcium supplementation and risk of cardiovascular disease: A systematic review and meta-analysis of cohort studies and randomized controlled trials. J Am Coll Nutr. 2020 May-Jun;39(4): 352-370.
Additional references
11. Myung SK et al., Calcium Supplements and Risk of Cardiovascular Disease: A Meta-Analysis of Clinical Trials Nutrients 2021, 13, 368.
12. Mao PJ et al., Effect of calcium or vitamin D supplementation on vascular outcomes: a meta-analysis of randomized controlled trials. .Int J Cardiol. 2013 Oct 30;169(2):106-11.
13. Pana TA et al., Calcium intake, calcium supplementation and cardiovascular disease and mortality in the British population: EPIC‑norfolk prospective cohort study and meta‑analysis. European Journal of Epidemiology. (2021) 36: 669–683.
14. Reid IR et al., Randomized controlled trial of calcium in healthy older women. Am J Med. 2006 Sep;119(9):777-85.
15. Reid IR, et al. Randomized controlled trial of calcium supplementation in healthy, nonosteoporotic, older men. Arch Intern Med. 2008; 168: 2276–82.
16. Harris SS ad Dawson-Hughes B. Effects of Hydration and Calcium Supplementation on Urine Calcium Concentration in Healthy Postmenopausal Women. J Am Coll Nutr. 2015;34(4):340-6.