CALCIUM INTAKE AND FRACTURE RATE

 

A Response

 

 

That osteoporosis / hip fracture rates are lowest in those countries where the least calcium is consumed, has bothered official institutes for quite some time.

They found a simple remedy; one shall not compare one country with another.

A response:

 

It has been argued in the past that certain osteoporosis fractures (e.g. hip) occur with greater frequency in countries with high calcium intakes than in countries with low intakes, and that therefore calcium cannot be important for bone health, at least at intakes above the levels found in the countries with the low calcium intakes, such as China (Abelow et al, Calcif Tissue Int 50: 14-18, Hegsted DM, J. Nutr. 116: 2316-2319, 1986)

 

This argument was considered and rejected at several expert levels: the NIH Consensus Conference on Osteoporosis in 1984 (JAMA 252: 799-802, 1984), the FDA review that led to the health claim for calcium rich foods in 1992 (Heaney RP. Evaluation of Publicly Available Scientific Evidence Regarding Certain Nutrient-Disease Relationships: Calcium and Osteoporosis. Prepared for Food Safety and Applied Nutrition, FDA Contract no, 223-88-2124, 1991), and the 1994 Consensus Conference on Optimal Calcium Intake (JAMA 272; 1942-1948, 1994)

 

Briefly, it is now recognized that hip fracture is a function not just of bone density but of the way people fall, of patterns of loading the hip (e.g. squatting), and of such structural features as hip axis length (Cumming et al, Osteoporosis Int. 4: 226-229, 1994), many of which vary across cultures.

 

For example, hip fracture risk doubles with each standard deviation increase in hip axis length, keeping bone mass constant. Adult Orientals today have shorter hip axes than adult Caucasians and thus, for the same bone mass, a lower hip fracture risk. This is just one of several reasons why cross-cultural comparisons, such as those cited above, may lead to erroneous conclusions.

 

Instead, it is necessary to examine the relationships between the purported independent variable and the outcome variable within an ethnic, national grouping. When this is done with the Chinese, for example, the same relationship between calcium intake and bone mass or fracture emerges as has been shown in Caucasians. Lau et al, (Incidence and risk factors for hip fractures in Hong Kong Chinese. In: Osteoporosis 1990. Eds. C. Christiansen, K. Overgaard. Copenhagen: Osteopress ApS, pp. 66-70, 1990) for example, have extensively documented a growing epidemie of hip fracture among Hong Kong Chinese, with the age specific fracture rate more than doubling between the mid 60’s and the mid 80’s. The only correlates found to be associated with increased risk of fractures were decreased physical activity and low calcium intake. Similarly, Hu et al, (Am J clin Nutr. 58 : 219-227, 1993) have shown that forearm bone mass in five rural Chinese countries varies directly with habitual calcium intake, just as has been shown in Europe and North America in Caucasian populations.

 

Finally, it must be stressed that other dietary influences (discussed elsewhere in this chapter) greatly influences the calcium requirement, and seeming ethno-culture differences in requirement cannot be evaluated without adjusting for these confounding effects. Thus, populations with low protein, sodium, and acid ash intakes will be predicted to have a lower calcium requirement than populations with higher intakes of these dietary components. This effect can be substantial. Nordin et al, (J Nutr 123; 1615-1622, 1993) has calculated low protein, sodium and acid ash diets may compatible with a requirement as low as 500 mg, whereas more typical Western diets raise the requirements presented in this chapter relate to a North American population consuming its typical diet, and are not intended to be applicable to Homo Sapiens generally.

 

 

 

 

Comments

 

 

In comment on the following phrase:

 

“In: Osteoporosis 1990. Eds. C. Christiansen, K. Overgaard. Copenhagen: Osteopress ApS, pp. 66-70, 1990) for example, have extensively documented a growing epidemie of hip fracture among Hong Kong Chinese, with the age specific fracture rate more than doubling between the mid 60’s and the mid 80’s. The only correlates found to be associated with increased risk of fractures were decreased physical activity and low calcium intake”.

 

What they did not mention, was that in Hong Kong:

in 1961, 25 kg milk / cap was consumed

in 1966, 22 kg milk / cap

in 1981, 39 kg milk / cap

in 1989, 45 kg milk / cap

 

It would be very interesting to know how much they consumed before 1961 (which is not available in the FAO database).

 

Wasn’t the question: “Why don’t the Chinese drink milk?” standard in anthropology courses?

 

 

 

“Nordin et al, (J Nutr 123; 1615-1622, 1993) has calculated low protein, sodium and acid ash diets may compatible with a requirement as low as 500 mg, whereas more typical Western diets raise the requirements”

 

Suppose for a second that Caucasians need 2000 mg calcium and Chinese need 500 mg daily: Caucasians averagely should consume at least 4 fold more calcium than Chinese to match Chinese hip-fracture incidence.

But in the US and Northern Europe 31 to 46 fold more milk is consumed, and hip-fracture incidence is over 6 fold higher than in China. (1)

 

 

 

 

R. Showalter, a highly respected and well know mathematician, commented on the following phrase:

 

"For example, hip fracture risk doubles with each standard deviation increase in hip axis length, keeping bone mass constant. Adult Orientals today have shorter hip axes than adult Caucasians and thus, for the same bone mass , a lower hip fracture risk."

 

So, if you lengthen the hip axis without increasing bone mass you've got a more fragile structure, with its structural material spread over more area, when, to increase length, for the same sturdiness, mass needs to increase more than in proportion to hip axis. Going in the other direction, for the same bone mass, on a smaller hip girdle, you get a more sturdy structure. (Galeleo wrote about this one)

Who says the bone mass is constant in the two cases? That's highly unlikely.

If hip axis increases N-fold, for the same sturdiness, you need bone mass to increase as the cube of N, not stay constant. And typically, that's what happens. Odds of finding a population, with matched bone masses but significantly different hip section geometries is unlikely - I can't believe that this test ever got run.



Source

 

(1) Xu. L. et al, Very low rates of hip fracture in Beijing, People's Republic of China ; The Beijing Osteoprosis Project. Am.J.Epedemiol. 1996 / 144 (9) / 901-907.

 

 

 



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