Heart, Stroke, Women's Health | September 30, 2014 | Author: The Super Pharmacist
Calcium is a mineral that the body needs for numerous functions, including building and maintaining bones and teeth, blood clotting, the transmission of nerve impulses, and the regulation of the heart’s rhythm. Ninety-nine percent of the calcium in the human body is stored in the bones and teeth. The remaining one percent is found in the blood and other tissues.
The calcium contained in bones is similar to a bone bank. The calcium from foods we eat is "deposited" into our bones and makes up our "bone bank." When our calcium intake is too low to maintain blood calcium at normal levels, our bodies will "withdraw" the calcium they need from our bones. Over time, if more calcium is taken out of the bones than is put in, the result may be a condition called osteoporosis which causes thin, weak bones that break easily.
Calcium cannot be manufactured by the body, so it is important to consume enough calcium to reduce the amount that the body has to borrow from bone.
Calcium supplements alone do not reduce the risk of fracture due to osteoporosis nor do vitamin D supplements alone. This is not surprising because the negative calcium balance in older people is often the result of both low calcium intake and vitamin D deficiency.
Calcium and vitamin D supplements shows no benefit in people with a normal or slightly negative calcium balance, but are indicated in people at high risk of fracture due to calcium and vitamin deficiency. This includes the elderly (>75 years) and institutionalised people. In this group, trials have convincingly shown a lower risk of fracture with supplementation therapy. On average, supplementation reduced the risk of non–vertebral fractures (including hip fractures) by 10–20%.
Patients with osteoporosis who are receiving treatment with osteoporosis medications have traditionally been advised to take calcium and vitamin D supplements as well. The efficacy of bisphosphonates, as well as all other osteoporosis drug treatments, has been predicated on sufficient intake of calcium, and it has been thought that bisphosphonate therapy could not be optimised without it. All studies that formed the basis for FDA approval of bisphosphonates in the treatment of osteoporosis had a protocol ensuring a certain minimum level of calcium intake or supplementation.
Osteoporosis medications include, among others, diphosphonates, selective estrogen receptor modulators, calcitonin, denosumab, and oestrogens.
Interestingly, however, a number of studies have also demonstrated the efficacy of osteoporosis agents administered without calcium supplements in preventing fractures. According to a recent study, baseline dietary calcium intake and vitamin D status did not alter the effects of zoledronate, suggesting that co-administration of calcium and vitamin D with zoledronate may not be necessary for individuals who are not at risk of marked vitamin D deficiency.
The benefits of calcium and vitamin D supplements for people between the ages of 50 and 75 without other risk factors for osteoporosis are supported by several studies and meta-analyses.
Results from the Women's Health Initiative study which included 36,282 postmenopausal women, half of whom were assigned to supplementation (1000 milligrams of calcium carbonate combined with 400 IUs of vitamin D3) showed a 12 percent reduction in the incidence of hip fracture which was determined not to be statistically significant. However, this trial, which lasted seven years, had a significant non-compliance rate. At the end of the trial, only 59 percent of the women participants were taking 80 percent or more of the study medication. Among the women who were adherent (i.e., those who took at least 80 percent of their study medication), calcium with vitamin D supplementation resulted in a significant 29 percent reduction in hip fracture.
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. Their recommendation is based on evidence that supplementation with calcium plus vitamin D prevents fractures in frail elderly people, particularly women in residential care.
An updated recommendation by the United States Preventive Services Task Force (USPSTF) concluded 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.
Until recently, it had been widely thought that, apart from causing constipation and gastrointestinal symptoms, use of calcium supplements did not cause adverse effects.
Controversy over calcium supplements arose when a trial by Dr. Mark J. Bolland of the University of Auckland suggested that calcium supplements might be associated with cardiovascular complications.
Since these results were based on small absolute numbers of events (34 myocardial infarctions and 57 strokes) which affected the study power, a meta-analysis was performed by the same authors. This meta-analysis included more than 12,000 individuals from 15 randomised placebo–controlled trials of calcium supplements (≥ 500 mg daily). An increase in the incidence of myocardial infarction of about 30% was seen in the calcium group when compared with the placebo group.
In a second meta-analysis by Bolland et al., the cardiovascular risk of combined calcium and vitamin D supplementation was examined. This meta-analysis, which included three randomised placebo-controlled trials, showed that calcium and vitamin D significantly increased the risk of myocardial infarction and the composite endpoint of myocardial infarction and stroke.
The results of this meta-analysis are dominated by a re-analysis of the Women's Health Initiative clinical trial. 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. Among studies that evaluated cardiovascular outcomes, no significant associations were found between calcium intake and cardiovascular events.
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).
Other studies fail to demonstrate an association between calcium and vitamin D supplements and cardiovascular risk.
The mechanisms by which calcium supplements might increase the cardiovascular risk remain speculative. Since high dietary calcium intake, which hardly affects serum levels of calcium, was not associated with an increased risk, the negative effect of calcium supplements might be explained by the fact that supplements acutely elevate serum calcium, which may enhance vascular calcification. High serum calcium might also be associated with increased coagulability and arterial stiffness.
There is limited evidence from studies investigating dietary calcium to demonstrate an increased risk of cardiovascular events with dietary calcium intake in postmenopausal women. For best clinical practice, an adequate daily dietary calcium intake in elderly people is recommended 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.
All researchers agree that, given the widespread use of supplemental calcium, better studies are needed to clarify possible risks and benefits, and to whom they may apply. Until such information is available, consumers seeking to preserve their bones would be wise to rely primarily on dietary sources of the mineral and to pursue regular weight-bearing or strength-building exercises, or both. Walking, running, weight lifting and working out on resistance machines is unquestionably effective and safe for most adults, if done properly.
Furthermore, the National Osteoporosis Foundation maintains that the findings of current studies and advice about supplements should “not apply to women with osteoporosis or broken bones after age 50 or those with significant risk factors for fracture.” For them, the benefits of calcium supplements are likely to far outweigh any risks.
Milk, yogurt, and cheese are rich natural sources of calcium. Non-dairy sources include vegetables, such as Chinese cabbage, kale, broccoli, and spinach. Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because people consume them frequently. Foods fortified with calcium include many fruit juices, tofu, and cereals.
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