Dairy products, calcium, and 1,25-dihydroxyvitamin D3 concentrations

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Dear Sir:

The report by Chan et al (1) on the intake of dairy products and dairy calcium in relation to plasma concentrations of 1,25-dihydroxyvitamin D₃ does not take into account the enhancement of calcium absorption by lactose. This action of lactose has been known since as long ago as 1929 and is attributable to an increased facilitated absorption in the ileum, which is unregulated, although the rise in circulating calcium may lead to a decrease in the regulated duodenal absorption of protein-bound calcium (2).

The lower concentration of 1,25-dihydroxyvitamin D₃ in the men with the high intake of dairy products may have been due, at least partly, to their greater absorption of lactose-enhanced calcium. This possibility is supported by the stronger inverse association of skim milk calcium than of dairy calcium with the concentration of 1,25-dihydroxyvitamin D₃, because skim milk has a greater lactose content than does whole milk.

Chan et al included the calcium intake from cheese in their dietary assessment; however, they did not report its association with the concentration of 1,25-dihydroxyvitamin D₃. Most cheeses are lacking in lactose, so I would not expect cheese calcium to show a significant inverse association with 1,25-dihydroxyvitamin D₃. The authors should have published their findings for cheese calcium.

Unregulated calcium absorption with retention as a result of a high intake of lactose is one explanation proposed for the epidemiologic suspicion that a high intake of lactose might be a dietary risk factor for ischemic heart disease (3). A common mode of action of calcium retention in lesions of atherosclerosis and adenocarcinoma of the prostate, particularly metastatic disease, might be the stimulation of cells with an osteoblastic potential.

REFERENCES

1. Chan JM, Stampfer MJ, Ma J, Gann PH, Gaziano JM, Giovannucci EL. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. Am J Clin Nutr 2001;74:549–54.
2. Pansu D, Bellaton C, Bronner F. Effect of lactose on duodenal-binding protein and calcium absorption. J Nutr 1979;109:508–12.
3. Segall JJ. Epidemiological evidence for the link between dietary lactose and atherosclerosis. In: Colaco CALS, ed. The glycation hypothesis of atherosclerosis. Austin, TX: Landes Bioscience, 1997:185–209.