ARCHIVED - Health Canada Scientific Summary on the U. S. Health Claim Regarding Calcium and Osteoporosis
Bureau of Nutritional Sciences
Food Directorate, Health Products and Food Branch
The objective of this summary is to review the scientific literature on the relationship between calcium intake and osteoporosis that has been published since the health claim was adopted by the U.S. Food and Drug Administration in 1993. For this health claim, two Canadian scientists recognized as experts in this field were contracted by Health Canada to independently evaluate the scientific literature. Studies identified in the Dietary Reference Intakes (DRI) report relating to the role of calcium in osteoporosis, in bone mineral density or bone mineral content and in fracture rates as well as studies published subsequent to the DRI Report were reviewed and included in the present summary report.
Osteoporosis is a disease characterized by low bone mass and micro architectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk. Peak bone mass is the major factor determining the risk of developing osteoporosis and by about age 20, the human skeleton has reached 90-95% of its peak bone mass, with the final 5-10% of bone mineral added during the next 10 years. People who have achieved a greater peak bone mass are less susceptible to osteoporosis. An estimated 1.4 million Canadians are believed to have osteoporosis, one in four women and one in eight men over 50 years of age. One Canadian survey has estimated the 1993 total health care costs (hospitalization, patient care, drug therapy) attributable to osteoporosis at $465 million and when long term facility care and chronic hospital care were included, the total reached $1.3 billion annually.
No national data on the calcium intakes of Canadians are available, although data from the Nova Scotia and Quebec Provincial surveys have reported relatively recent data for calcium intakes (data were obtained from surveys conducted in 1990). Mean calcium intake data for these provinces ranged from about 770 to 1160 and 574 to 788 mg/d (depending on age) for males and females respectively, with intakes declining with increasing age.
Controlled clinical trials of calcium supplementation have been conducted for almost every age group (children and older) and for the most part support the calcium and osteoporosis health claim.
In children, clinical trials have shown a modest but positive effect of calcium supplementation, particularly in those children with intakes <1000 mg/d, on bone mineral accretion. Similar benefits have been seen with calcium intakes >1000 mg/d. In general, supplementation resulted in 1 to 5% greater gains in bone mineral density or bone mineral content compared to controls. However the long term benefits of such an increase and whether the increase is sustained, remain unclear at the present time.
Data concerning the role of calcium in bone health in young adults is particularly lacking compared to other age groups. No recent clinical trials in this age group were found and observational studies, although suggestive of a benefit, were not consistent. A small but significant correlation between calcium intake and bone mass was found in a meta analysis of 24 observational studies. Physical activity appears to be a significant determinant of bone health in this age group.
The studies reviewed in the DRI report and those conducted since the DRI report show several consistent effects regarding the role of calcium in bone loss in post menopausal women. Early post menopausal women are less responsive to calcium supplementation than late post menopausal women; where effects were seen, they tend to be in cortical bone, with spine less responsive to calcium. Late menopausal women with low calcium intakes tend to gain more BMD from calcium supplementation than do women with higher usual intakes of calcium. Observational studies in post menopausal women and one study which included men generally indicated a positive effect of calcium on bone density. Several studies also suggested that higher intakes of calcium earlier in life were related to reduced incidence of fractures or increased BMD in post menopausal women.
Many studies conducted in the elderly have shown a benefit of supplements or higher intakes of calcium on the clinically important outcome - fracture rate. Almost half of the trials in the elderly found decreased fracture incidence, in addition to changes in BMD. More studies in this age group than in any other have included male subjects and benefits appeared to apply equally to men. In the elderly, most studies have provided a supplement of vitamin D along with calcium. Given that vitamin D deficiency is most prevalent among the elderly, particularly among institutionalized or house bound individuals, it appears important that they have adequate vitamin D in order to utilize calcium or to benefit from additional calcium.
Based on this evidence, several elements are required for this health claim:
- The reference to a healthy diet to provide all the nutrients necessary for proper bone formation (protein, minerals, vitamins, and essential fatty acids) should be included.
- Calcium alone will not prevent bone loss in the absence of weight bearing exercise and several of the recent studies and the recent meta analysis by Kelley (1998) affirm maintaining the link with exercise in this claim.
- There is sufficient evidence that calcium at or near levels recently recommended by the 1997 DRI Panel provides additional bone mass in children and adolescents and reduces bone loss in older adults. Since the DRI Panel has named its recommendations as Adequate Intake, the term "adequate calcium" would be preferable to "enough calcium".
- There is evidence that adequate calcium during childhood can promote more bone formation and that during later adult life, particularly during late post menopause and in the elderly, calcium can protect against bone loss and fractures. Therefore, the claim should not be restricted to teens and young adults.
- Reference to any specific ethnic group is not justified for Canada: it is likely that all ethnic groups have some risk and there is little information on calcium intakes and effects on bone parameters in groups such as First Nations, East Indians and many others.
- As indicated by the DRI Panel and results in the elderly, there is no evidence of a specific gender effect in need for calcium (although there are fewer studies conducted in men than in women). Therefore, gender need not be specified.
- The term "osteoporosis" is in common usage due to publicity by groups such as the Osteoporosis Society of Canada and use of this term should not impede the understanding of this claim.
- Vitamin D is important, particularly in older adults and in children, in enabling them to adequately use calcium and should be part of this health claim. Children in Canada likely receive adequate vitamin D through fortification of milk and margarine and through sunlight exposure, however, for older adults who require 10 µg/d (age 51-70) to 15 µg/d (age >70), which are double and triple, respectively, the recommended intakes for younger age groups, dietary sources are vital. This statement may prevent over focussing on calcium at the expense of other nutrients, particularly vitamin D. Foods bearing a health claim for calcium must contain at least 200 mg calcium per reference amount and per serving of stated size.
Based on a review of the evidence related to the various claim elements, the following health claim is proposed for Canada:
A healthy diet with adequate calcium and regular exercise may help to achieve strong bones in children and adolescents and may reduce the risk of osteoporosis in older adults. An adequate intake of vitamin D is also necessary.
The following compositional criteria are proposed for foods bearing this claim: the food must provide at least 200 mg calcium per serving of stated size and the phosphorus content (excluding that provided by phytate) must be less than the calcium content.*
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