Fact: The calcium in milk is well absorbed and drinking milk does not cause calcium to be leached from the body.
Drinking milk does not cause calcium to be leached from the body
Drinking milk and osteoporosis risk
Drinking milk does not cause calcium to be leached from the body It has been suggested that the consumption of milk and milk products increases the rate of calcium loss from the body, thereby increasing the risk of osteoporosis. This suggestion is based on the notion that the high protein content of milk causes a net loss of calcium from the body via the urine. The misconception is compounded by misinterpretation of data concerning urinary calcium excretion and the inference that poor absorption of calcium from milk is the cause.
Several studies have confirmed that calcium is well absorbed from milk (Gueguen, 2000; Recker, 1988) and that the absorption is better than that from most vegetable foods (Weaver, 1999; Fairweather-Tait, 1989). At least two factors in milk-lactose and casein could be responsible for promoting calcium absorption and causing this higher bioavailability.
In Western societies, it is normal for small amounts of calcium (typically 150 mg) to be lost daily in the urine. Proteins rich in sulphur amino acids (cysteine and methionine) promote urinary calcium excretion because the excretion of sulphur makes the urine relatively acid and therefore fosters calcium loss (Marsh, 1988). However, this effect of protein occurs to varying degrees across the range of protein intakes, not just with high intakes (Heaney, 1993), and the effect is minimal with the typical levels of protein intake normally seen (Spencer, 1988). The truth is that the high calcium/protein ratio in dairy products (36 mg calcium: 1 g protein) particularly favours calcium retention and thus promotes an increase in bone mass (Chan, 1995; Heaney, 1998).
In addition, among elderly people, a low protein/low phosphorus diet may have adverse effects on calcium balance (Spencer, 1988), which is a good reason for promoting milk consumption for this age group.
It has also been shown that a high intake of sodium chloride (salt) results in increased absorption of sodium, increased levels of urinary sodium and increased obligatory loss of calcium (Kurtz, 1987; Goulding, 1997). Indeed, urinary sodium is known to be an important determinant of urinary calcium excretion in children and adolescents (Matkovic, 1995; O'Brien, 1996). Furthermore, a loss of 10 mg of calcium in the urine of postmenopausal women has been reported for every 500 mg of sodium (as sodium chloride) consumed (Nordin and Polley, 1987). Although a positive association has been found between dietary sodium intake and urinary calcium excretion, the benefit of a reduction in sodium intake on bone loss and fracture rates has yet to be clarified. Recent evidence suggests that when sodium intake increases urinary calcium, there is an adaptation in dietary calcium absorption, which compensates for and prevents increased bone resorption or turnover (Ginty, 1998).
Drinking milk and osteoporosis risk
Calcium intake influences the risk of osteoporosis by affecting genetically determined peak bone mass, which is reached by age 30 or earlier. A recent cross-sectional study in young women aged 18 to 31 years found that higher milk (and calcium) intake during adolescence is associated with greater bone mineral measures at various sites during development of peak bone mass (Teegarden, 1999). Adequate intakes of calcium, by influencing bone mass, also helps to reduce the risk of fractures in children and adolescents. Even in later years, increasing calcium or food sources of calcium maintains bone mass, reduces bone loss, and helps to lower the risk of osteoporosis. A recent multi-center, randomized controlled trial found that when healthy adults aged 55 to 85 years increased their calcium intake by more than 750 mg/day by consuming more dairy foods for 12 weeks, bone resorption significantly decreased (Heaney, 1999). Reducing bone resorption is the first step in maintaining bone density. An adequate intake of calcium also augments the effectiveness of hormonal and pharmacologic regimens to treat osteoporosis.
A recent analysis of 139 papers on the role of calcium in skeletal health published over the past 25 years provides convincing evidence for calcium's benefits (Heaney, 2000). In all but two of 52 investigator-controlled calcium intervention studies, increasing calcium intake improved bone balance, increased bone gain during growth, reduced bone loss in later years, or lowered fracture risk. Similar beneficial effects of calcium were found in approximately three-quarters of 86 observational studies, most of which used dairy products as a source of calcium (Heaney, 2000). Although many factors, nutritional and non-nutritional, contribute to bone health, the impact of calcium is clearly large.
Drinking milk and osteoporosis risk
Drinking milk does not cause calcium to be leached from the body It has been suggested that the consumption of milk and milk products increases the rate of calcium loss from the body, thereby increasing the risk of osteoporosis. This suggestion is based on the notion that the high protein content of milk causes a net loss of calcium from the body via the urine. The misconception is compounded by misinterpretation of data concerning urinary calcium excretion and the inference that poor absorption of calcium from milk is the cause.
Several studies have confirmed that calcium is well absorbed from milk (Gueguen, 2000; Recker, 1988) and that the absorption is better than that from most vegetable foods (Weaver, 1999; Fairweather-Tait, 1989). At least two factors in milk-lactose and casein could be responsible for promoting calcium absorption and causing this higher bioavailability.
In Western societies, it is normal for small amounts of calcium (typically 150 mg) to be lost daily in the urine. Proteins rich in sulphur amino acids (cysteine and methionine) promote urinary calcium excretion because the excretion of sulphur makes the urine relatively acid and therefore fosters calcium loss (Marsh, 1988). However, this effect of protein occurs to varying degrees across the range of protein intakes, not just with high intakes (Heaney, 1993), and the effect is minimal with the typical levels of protein intake normally seen (Spencer, 1988). The truth is that the high calcium/protein ratio in dairy products (36 mg calcium: 1 g protein) particularly favours calcium retention and thus promotes an increase in bone mass (Chan, 1995; Heaney, 1998).
In addition, among elderly people, a low protein/low phosphorus diet may have adverse effects on calcium balance (Spencer, 1988), which is a good reason for promoting milk consumption for this age group.
It has also been shown that a high intake of sodium chloride (salt) results in increased absorption of sodium, increased levels of urinary sodium and increased obligatory loss of calcium (Kurtz, 1987; Goulding, 1997). Indeed, urinary sodium is known to be an important determinant of urinary calcium excretion in children and adolescents (Matkovic, 1995; O'Brien, 1996). Furthermore, a loss of 10 mg of calcium in the urine of postmenopausal women has been reported for every 500 mg of sodium (as sodium chloride) consumed (Nordin and Polley, 1987). Although a positive association has been found between dietary sodium intake and urinary calcium excretion, the benefit of a reduction in sodium intake on bone loss and fracture rates has yet to be clarified. Recent evidence suggests that when sodium intake increases urinary calcium, there is an adaptation in dietary calcium absorption, which compensates for and prevents increased bone resorption or turnover (Ginty, 1998).
Drinking milk and osteoporosis risk
Calcium intake influences the risk of osteoporosis by affecting genetically determined peak bone mass, which is reached by age 30 or earlier. A recent cross-sectional study in young women aged 18 to 31 years found that higher milk (and calcium) intake during adolescence is associated with greater bone mineral measures at various sites during development of peak bone mass (Teegarden, 1999). Adequate intakes of calcium, by influencing bone mass, also helps to reduce the risk of fractures in children and adolescents. Even in later years, increasing calcium or food sources of calcium maintains bone mass, reduces bone loss, and helps to lower the risk of osteoporosis. A recent multi-center, randomized controlled trial found that when healthy adults aged 55 to 85 years increased their calcium intake by more than 750 mg/day by consuming more dairy foods for 12 weeks, bone resorption significantly decreased (Heaney, 1999). Reducing bone resorption is the first step in maintaining bone density. An adequate intake of calcium also augments the effectiveness of hormonal and pharmacologic regimens to treat osteoporosis.
A recent analysis of 139 papers on the role of calcium in skeletal health published over the past 25 years provides convincing evidence for calcium's benefits (Heaney, 2000). In all but two of 52 investigator-controlled calcium intervention studies, increasing calcium intake improved bone balance, increased bone gain during growth, reduced bone loss in later years, or lowered fracture risk. Similar beneficial effects of calcium were found in approximately three-quarters of 86 observational studies, most of which used dairy products as a source of calcium (Heaney, 2000). Although many factors, nutritional and non-nutritional, contribute to bone health, the impact of calcium is clearly large.
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Ph.D., Justus liebig University, Giessen, West Germany. Professor,Department of Food Science. University of Ain Shams. Cairo, Egypt. Expert and consultant(dairy, food, water and nutrition |
