Some types of colorectal cancer seem to be caused by genetic factors, while others appear to be influenced by dietary factors.

 

In humans, controlled clinical trials have found modest decreases in the risk of colorectal cancer with calcium supplementation of 1,200–2,000 mg/day (5, 6, 7). A pooled analysis of ten prospective cohort studies, including 534,536 men and women, found that those with the highest calcium intake (1,087 mg/day from food and supplements) had a 22% lower risk of colorectal cancer compared to those with the lowest intake (732 mg/day) (8).

 

However, most large prospective studies have reported increased calcium intakes are only weakly associated with a decreased risk of colorectal cancer, which might be explained by the presence of groups within the population that differ in their response to calcium (9).

 

Before conclusions can be drawn, more research is needed to clarify whether specific subgroups in the larger population have different calcium requirements with respect to decreasing the risk of colorectal cancer.

 

Osteoporosis

Osteoporosis, a multifactorial skeletal disorder in which bone strength is compromised, is most commonly diagnosed in white postmenopausal women (10). Strategies for reducing the risk of osteoporotic fracture include the attainment of maximal peak bone mass and the reduction of bone loss later in life. Although calcium is the nutrient consistently found to be most important for attaining peak bone mass and preventing osteoporosis, adequate vitamin D intake is also required for optimal calcium absorption.

 

There is evidence to suggest that high impact activity (e.g., running) and resistance exercise (weights) in the presence of adequate calcium (1,200 mg/day) and vitamin D (600 IU/day) intake early in life contributes to the attainment of higher peak bone mass (11, 10, 12). Lower impact exercise (e.g., walking, swimming, and cycling) have beneficial effects on other aspects of health and function, but their effects on bone loss are minimal. However, exercise later in life, even beyond 90 years of age, can still increase strength and reduce the likelihood of a fall, another important risk factor for hip fracture (10).

 

Kidney stones

The cause of kidney stones is usually unknown. However, abnormally elevated urinary calcium increases the risk of developing calcium stones. Dietary factors such as salt (sodium chloride), protein, and calcium are known to increase urinary calcium (13, 14).

 

A randomized controlled trial in 36,282 postmenopausal women reported that a combination of supplemental calcium (1,000 mg/day) and vitamin D (400 IU/day) was associated with a significantly increased risk of kidney stones (15).

 

Although calcium stone formers have been advised to restrict calcium intake in the past, a cross-sectional study in 282 patients with calcium oxalate stones found that dietary salt was the factor most strongly associated with urinary calcium excretion (16); this led the authors to suggest that reduced salt intake should be recommended for calcium stone-forming patients (17).

 

At present, the only dietary change proven effective in reducing kidney stone recurrence is increasing fluid intake.

 

Further controlled trials are necessary to determine whether supplemental calcium affects the development of kidney stones.

 

Pregnancy-induced hypertension

Pregnancy-induced abnormally high blood pressure ('hypertension') occurs after the 20th week in 10% of pregnancies and is a major health risk for pregnant women and their unborn children. In addition to pregnancy-induced hypertension (PIH), preeclampsia includes the development of severe swelling (edema) and protein in the urine ('proteinuria') (18). Although the cause of PIH is not entirely understood, calcium metabolism appears to play a role.

 

Data from epidemiological studies suggest a relationship between low calcium intake and an increased incidence of PIH, but the results of experimental research on calcium supplementation and PIH have been less clear. A review of randomized controlled studies found that calcium supplementation reduced the incidence of high blood pressure in pregnant women at high risk of PIH, as well as in pregnant women with low dietary calcium intake (19).

 

However, a large clinical trial of Calcium for Preeclampsia Prevention (CPEP) in over 4,500 pregnant women found no effect of a mean intake of 2,300 mg/day supplemental calcium on PIH (20).

 

For the general population, meeting current intake recommendations for calcium intake during pregnancy may help prevent PIH. Further research is required to determine whether women at high risk for PIH would benefit from calcium supplementation above the current recommendations.

 

Stroke

In an epidemiological study, women who took in more calcium, both through their diet and with supplements, were less likely to have a stroke over a 14-year period (21).

 

More research is needed to confirm potential benefits.

 

Lead toxicity

Children who are chronically exposed to lead, even in small amounts, are more likely to develop learning disabilities, behavioral problems, and to have low IQs. Abnormal growth and neurological development may occur in the infants of women exposed to lead during pregnancy. In adults, lead toxicity may result in kidney damage and high blood pressure (22). Adequate calcium intake could protect against lead toxicity by decreasing the uptake of lead in the digestive tract and by preventing exposure to lead accumulated in the skeleton and mobilized through bone loss (resorption). 

 

A study of blood lead levels during pregnancy found that women with inadequate calcium intake during the second half of pregnancy were more likely to have elevated blood lead levels, probably related to increased bone resorption with the release of accumulated lead into the blood (23). Additionally, in postmenopausal women, increased calcium intake has been associated with decreased blood lead levels (24).