Home | Site Map | Contact Us| Reference
 |
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Calcium
Calcium's role in health and disease prevention
Calcium and bone health
Your bones are living tissues and continue to change throughout life. During childhood and adolescence, bones increase in size and mass. Bones continue to add more mass until around age 30, when peak bone mass is reached. Peak bone mass is the point when the maximum amount of bone is achieved.
Because bone loss, like bone growth, is a gradual process, the stronger your bones are at age 30, the more your bone loss will be delayed as you age. Therefore, it is particularly important to consume adequate calcium and vitamin D throughout infancy, childhood, and adolescence. It is also important to engage in weight-bearing exercise to maximize bone strength and bone density (amount of bone tissue in a certain volume of bone) to help prevent osteoporosis later in life. Weight bearing exercise is the type of exercise that causes your bones and muscles to work against gravity while they bear your weight. Resistance exercises such as weight training are also important because they help to improve muscle mass and bone strength.
Examples of weight bearing exercise
walking
running
dancing
aerobics
skating
Examples of NON-weight bearing exercise
swimming
bicycling
water aerobics
Osteoporosis is a disorder characterized by porous, fragile bones. It is a serious public health problem for more than 10 million Americans, 80% of whom are women. Another 34 million Americans have osteopenia, or low bone mass, which precedes osteoporosis. Osteoporosis is a concern because of its association with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones [22]. Each year, Americans suffer from 1.5 million fractures because of osteoporosis [23].
Osteoporosis and osteopenia can result from dietary factors such as [11,24,25]:
chronically low calcium intake
low vitamin D intake
poor calcium absorption
excess calcium excretion
When calcium intake is low or calcium is poorly absorbed, bone breakdown occurs because the body must use the calcium stored in bones to maintain normal biological functions such as nerve and muscle function. Bone loss also occurs as a part of the aging process. A prime example is the loss of bone mass observed in post-menopausal women because of decreased amounts of the hormone estrogen. Researchers have identified many factors that increase the risk for developing osteoporosis. These factors include being female, thin, inactive, of advanced age, cigarette smoking, excessive intake of alcohol, and having a family history of osteoporosis [26].
In 1993 the FDA authorized a health claim for food labels on calcium and osteoporosis in response to scientific evidence that an inadequate calcium intake is one factor that can lead to low peak bone mass and is considered a risk factor for osteoporosis [27]. The claim states that "adequate calcium intake throughout life is linked to reduced risk of osteoporosis through the mechanism of optimizing peak bone mass during adolescence and early adulthood and decreasing bone loss later in life".
Various bone mineral density (BMD) tests, including those that measure your hip, spine, wrist, finger, shin bone, and heel, can help determine bone mass. These tests provide a T-score which is a measure of bone mineral density that compares an individual's BMD to an optimal BMD of a 30 year old healthy adult. See Figure 2 below. A T-Score of -1.0 and above indicates normal bone density. A T-score of -1.0 to -2.5 indicates that a person is considered to have low bone mass (osteopenia). A score below -2.5 indicates osteoporosis [28].
Although osteoporosis affects people of different races, genders and ethnicities, women are at highest risk because their skeletons are smaller to start with and because of the accelerated bone loss that accompanies menopause. Adequate calcium and vitamin D intakes, as well as weight bearing exercise are critical to the development and maintenance of healthy bone throughout the lifecycle. Older adults should strive to maintain recommended daily calcium intakes as well as an adequate vitamin D intake.
Calcium and high blood pressure
Some observational studies (type of research study in which the treatment/intervention is observed and not controlled by the researchers) and experimental studies (type of research study in which the researchers control the treatments/interventions and that are assigned to participants) indicate that individuals who eat a vegetarian diet high in minerals (including calcium, magnesium and potassium) and fiber, and low in fat, tend to have reduced blood pressure [29-31].
Findings from some clinical trials (a specific type of experimental study) used to evaluate the effects of one or more treatments/interventions in humans) indicate that an increased calcium intake lowers blood pressure and the risk of hypertension (high blood pressure) [32,33]. However, the results of some studies produced small and inconsistent reductions in blood pressure. One reason for these results is because these research studies tended to test the effect of single nutrients rather than foods on blood pressure.
To help test the combined effect of nutrients including calcium from food on blood pressure, a study was conducted to investigate the impact of various dietary eating patterns on blood pressure. This study titled "Dietary Approaches to Stop Hypertension (DASH)" was reported in 1997 by the National, Heart, Lung and Blood Institute of the National Institutes of Health. It investigated the effect of various eating patterns on lowering blood pressure. The DASH study was a multi-center research trial where food was provided to over 450 adults. It examined the effects of three different diets on high blood pressure: a control, "typical American" diet and two modified diets (high fruits-and-vegetables and a combination "DASH" diet - high in fruits, vegetables, and low fat dairy). See Table 3 for a comparison of some of the components of the three diets.
Table 3: Comparison of the Three Diets Tested in the "DASH" StudyDiet Components Fruit & Vegetable Servings Lowfat Dairy Servings Calcium (mg) Fat (% of total calories) Sodium (mg) Cholesterol (mg) Fiber (g)
Control "Typical American" diet 3.5 0.1 450 37 3000 300 9
Fruits-and-Vegetables diet 8.5 0.0 450 37 3000 300 31
Combination "DASH" diet 9.5 2.0 1240 27 3000 150 31
Of the three diets tested, the combination "DASH" diet resulted in the greatest decrease in blood pressure [34]. Thus, this finding from a large and carefully executed clinical trial helped demonstrate that the combination "DASH" diet, with increased calcium, decreased blood pressure [35]. A number of further studies have been done, all showing a similar relationship between increasing calcium intakes and decreased blood pressure [36]. A study conducted after the original "DASH" study, referred to as the "DASH-Sodium" study showed that the DASH diet without sodium restriction provided as much blood pressure reduction as did severe sodium restriction on the control diet (1500 mg sodium/day) [37]. Overall it appears that consuming an adequate intake of fruits and vegetables as well as calcium from low fat dairy products plays a significant role in controlling blood pressure. Additional information and sample DASH menu plans are available on the National Heart, Lung and Blood Institute's Web site (http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/index.htm).
Calcium and cancer
Colorectal cancer
The relationship between calcium intake and the risk of colon cancer has not been conclusively determined. Observational and experimental research studies investigating the role calcium plays in the prevention of colon cancer show mixed results. Some studies suggest that increased intakes of dietary (low fat dairy sources) and supplemental calcium are associated with a decreased risk of colon cancer [38-41]. Supplementation with calcium carbonate is reported to lead to reduced risk of adenomas (nonmalignant tumors) in the colon, a precursor to colon cancer, but it is not known if this will ultimately translate into reduced cancer risk [42]. Another study reported on the association between diet and colon cancer history in 135,000 men and women participating in two large health surveys, the Nurses' Health Study and the Physicians' Health Study. The authors found that those who consumed 700 to 800 mg calcium per day had a 40 to 50% lower risk of developing left side colon cancer [43]. However, a few other observational studies found inconclusive evidence regarding any association of calcium intake with colon cancer [44-46]. Although some research findings indicate a protective effect of calcium or low fat dairy foods against colon cancer, further studies are necessary to confirm this role for calcium.
Prostate cancer
There is some evidence to suggest that higher calcium (ranging from 600 mg to >2000 mg of calcium) and/or dairy intakes (>2.5 servings) may be associated with the development of prostate cancer [47-50]. However, these studies are observational in nature rather than clinical trials and cannot establish a definite causal relationship between calcium and prostate cancer. Other findings only show a weak relationship, no relationship at all or the opposite relationship between calcium and prostate cancer [51-54]. Thus, the relationship between calcium intake, dairy intake and prostate cancer risk remains unclear. At the present time, it is recommended that men ages 19 and over consume a "modest" intake of calcium ranging from 1000-1200 mg per day and maintain an intake below the upper tolerable limit (2500 mg) [1].
Calcium and kidney stones
Kidney stones are crystallized deposits of calcium and other minerals in the urinary tract. Calcium oxalate stones are the most common form of kidney stones in the US. High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. However, more recent studies show that high dietary calcium intakes actually decrease the risk for kidney stones [55-57]. Other factors such as high oxalate intake and reduced fluid consumption appear to be more of a risk factor in the formation of kidney stones than calcium in most individuals [58].
Calcium and weight management
Research suggests that calcium, especially calcium derived from dairy products, may help to regulate body fat. Laboratory and animal studies provide initial evidence of calcium's role in decreasing body fat while other studies confirm this potential benefit for humans. At this time, lowfat dairy products seem more beneficial than calcium supplements alone in helping to reduce body fat and reduce weight [59-63]. However, larger studies in humans need to be conducted to help confirm the benefit of calcium for weight loss. Currently, The National Institutes of Health is conducting a small clinical trial to study the effects of supplemental calcium on body weight, body composition, blood lipids and obesity-related conditions such as insulin sensitivity. This clinical trial will be completed in late 2004.
What is the recommended intake for calcium?
Helping hints for meeting your calcium needs
What affects calcium absorption and excretion?
When can a calcium deficiency occur?
Is there a health risk of too much calcium?
