Optimal Amount of Dietary Calcium Intake and Benefits of Calcium Supplementation

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In the Stone Age the diet of human adults is estimated to have contained from 50 to 75mmol of Ca (2000-3000 mg)/day, three to five times the median calcium intake of the present day in Western countries.7 As the human genetic make-up has not modified, our body needs remain suited to a much higher calcium intake than we currently consume. Although mammalian physiology contains mechanisms by which organisms can adjust to temporary environmental shortages, chronic calcium retention has a number of health consequences. A number of chronic diseases have been linked to a low dietary calcium intake, including bone fragility, high blood pressure and colon cancer in susceptible individuals.8 Recent studies have also linked weight control and regulation of body fat to an adequate dietary calcium intake. We present here evidence indicating that an optimal dietary calcium intake may prevent to some extent each of these multifactorial problems.

Calcium is an essential nutrient and the natural diets of all mammals are rich in calcium. Calcium requirements vary throughout an individual's lifetime, with greater needs in three critical periods of life: (a) during the times of childhood and adolescence, (b) in women during pregnancy and lactation and (c) in later adult life (Table 6.1). From birth until about age 18, bones are forming and growing, and during late adolescence, through young adulthood, adult bone is formed and reaches its maximum strength and density. A sufficient calcium intake is essential to those processes. Pregnancy represents a significant physiological stress on calcium homeostasis. A full-term infant accumulates approximately 30 g of calcium during gestation, most of which is assimilated into the fetal skeleton during the third trimester. During lactation, 160-300 mg/day of maternal calcium is lost through production of breast milk. Later in life, aging is physiologically associated with several modifications of calcium metabolism (Table 6.2). It has been shown that an altered cellular ion metabolism is associated with aging,5,9 with a continuous age-dependent elevation of intracellular calcium and a reciprocal fall in serum ionized free calcium levels10 (Figure 6.2). Calcium intake, intestinal absorption and renal conservation all tend to decrease with age1,11 (Table 6.2), and may cause a state of negative calcium balance and of a progressive calcium deficiency in elderly subjects.

The Consensus Conference from the NIH has stated the recommended calcium intake throughout the different life periods (Table 6.3).12 On the basis of the most current information available, optimal calcium intake has been estimated to be 400 mg/day (birth to 6 months) to 600 mg/day (6-12 months) in

Table 6.2 Alterations of calcium metabolism associated with aging

Decreased calcium intake Decreased calcium absorption Increased intracellular calcium Decreased serum ionized calcium Increased serum levels of PTH Altered vitamin D status Decreased renal conservation Increased bone turnover Decreased physical activity

"D

Age (years)

Figure 6.2

Effect of aging on serum ionized calcium in normal subjects10

Table 6.3 Optimal daily calcium intake according to NIH consensus conference12

Age

mg/day

Neonates

0-6 months

400

6 months to 1 year

600

Children

1-5 years

800

6 10 years

800-1200

Adolescents

11 24 years

1200-1500

Male adults

25 65 years

1000

Elderly (>65 years)

1500

Female adults

20 25 years

1000

Pregnant and nursing

1200-1500

Postmenopausal (>50 years)

1500

Elderly (>65 years)

1500

infants; and 800 mg/day in young children (1-5 years) and 800-1200 mg/day for older children (6-10 years); 1200-1500 mg/day for adolescents and young adults (11-24 years). In adulthood the recommended intake is of around 1000 mg/day for women between 25 and 50 years and in adult men between 25 and 65 years. These suggested intakes increase in special situations to 12001500 mg/day for pregnant or lactating women, and to 1500 mg/day for post-menopausal women not on estrogen therapy. The recommended calcium needs also tend to increase in the elderly and has been estimated to be, for all women and men over 65, around 1500 mg/day.

Other factors play a role in calcium intake, including vitamin D, which is needed for adequate calcium absorption. In elderly men and women, an adequate calcium intake is of extreme importance. Indeed, in the older subjects the daily requirement is higher (1500mg/day) than in the young individual to counteract the age-related alterations of calcium balance regulatory mechanisms mentioned earlier (Table 6.2).

In contrast to the NIH suggestions to increase the calcium content in the diet, several studies have demonstrated that dietary calcium content tends to be reduced in men as well as in women with advancing age.13,14 In men and women 65 years of age and older, calcium intake of less than 600 mg/day (about one-third of the NIH recommendation) is common.12 Optimal calcium intake may be achieved through diet, calcium-fortified foods, calcium supplements or various combinations of these. Many factors can negatively influence calcium availability, such as certain medications or food components.

Osteoporosis

Several studies have addressed the possible role of calcium supplementation in the prevention and treatment of a number of chronic disorders. This includes in the first place the prevention and treatment of osteoporosis, and other bone diseases, but the role of calcium has been suggested also in the prevention and treatment of salt-sensitive and pregnancy-associated hypertension, and to reduce the development of precancerous changes in colon cancer. The purpose of this chapter is to review the possible role of dietary calcium supplementation in the therapy and/or in the prevention of calcium-deficiency-related diseases.

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