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Letters to the Editor |
Creighton University601 North 30th StreetSuite 4841Omaha, NE 68131E-mail: rheaney{at}creighton.edu
Dear Sir:
In the December 1998 issue of the Journal, Kung et al (1) presented calcium absorption data for Chinese women, in part in an attempt to determine whether recent Western calcium intake recommendations should apply to the Chinese and in part to explain the apparently lower calcium requirement of the Chinese. Kung et al report high calcium absorption in the Chinese women, which, at face value, might serve to explain how the Chinese seem to get by with lower calcium intakes than whites. However, Kung et al made 2 critical errors: the alleged difference in intakes between Chinese and Western populations is illusory and the absorption method chosen (a 100-mg Ca carrier load, as the chloride salt, without accompanying food) was not suitable for providing the desired information.
The Chinese women in this study had mean calcium intakes in the range of 554–561 mg/d, and when adjusted for body size, 10–11 mg•kg-1•d-1. Corresponding values for US women of the same age range in the second National Health and Nutrition Examination Survey (2) are virtually identical (541–571 mg/d) and, when adjusted for body size, are actually considerably lower, ie, 
8.4 mg•kg-1•d-1. In the third National Health and Nutrition Examination Survey (3), corresponding values are 711 mg Ca/d, reflecting increasing supplement use in the 1980s. However, even this value, when adjusted for body size, is slightly lower than that reported by Kung et al (10.0 mg•kg-1•d-1).
In 1989, Eastell et al (4) showed that the absorption method used by Kung et al did not correlate with true food absorption; hence, it was unsuitable to address the question Kung et al put to it. Although this method can be helpful in diagnosing calcium malabsorption (5), ie, in patients who would benefit from calcitriol therapy, it neither provides a quantitative estimate of food calcium absorption nor correlates with true absorption. [To accomplish such, the calcium tracer must be introduced into a food calcium source and ingested as a part of a meal (4).]
Finally, the alleged difference in absorption between the Chinese and Western women (60% in the Chinese women compared with 20–30% in the Western women) resulted from a proverbial comparison of apples and oranges. The lower values reported for Western women (6, 7) were derived by using a different calcium absorption method, which involved both a larger calcium load [a point Weaver (8) makes in her accompanying editorial] and co-ingestion of calcium and ordinary food. In the study by Eastell et al (4), in which the 2 calcium absorption methods were compared in Minnesotan white women, average calcium absorption with the method used by Kung et al was between 50% and 60%, not appreciably different from the values currently reported by Kung et al for contemporary Chinese women.
In conclusion, there appears to be virtually no difference between white and Chinese women in either calcium intake or absorption. The often cited fact that dairy consumption is low in China is irrelevant. It is low in US women as well.
FOOTNOTES
Editor's note: Kung et al chose not to respond to this letter.
REFERENCES
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