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American Journal of Clinical Nutrition, Vol. 87, No. 5, 1541, May 2008
© 2008 American Society for Nutrition

LETTER TO THE EDITOR

Reply to P Elwood et al

Qi Sun and Frank B Hu

Departments of Nutrition and Epidemiology
Harvard School of Public Health
665 Huntington Avenue
Boston, MA 02115

Dear Sir:

On the basis of the results of our study, we suggest that a higher intake of dairy fat, which primarily comprises saturated fat (1), may be associated with an elevated risk of ischemic heart disease (IHD). Because pentadecanoic acid (15:0) is a marker of dairy fat rather than of total dairy products, these results should not be interpreted as pertinent to the intake of nonfat dairy products, including skim milk. In our previous analyses of dietary data from the Nurses' Health Study, whole milk intake was associated with an increased risk of IHD, whereas skim milk intake was associated with a lower risk (2).

In the Caerphilly cohort study, only baseline milk intake was measured during 20–24 y of follow-up (3). Because of large day-to-day variations in dietary intakes, a single measurement is unlikely to capture long-term diet (4). In the Caerphilly cohort of elderly men, although milk intake was assessed 3 times (baseline and 5 and 10 y after baseline) during 20 y of follow-up, only 3 categories of intake frequency were listed in the questionnaire (<0.5, 0.5–1, and >1 pint/d), and no information on the type of milk (whole milk or skim milk, milk added in food or drink, etc) was obtained (5). Thus, these analyses cannot distinguish the effects of different types of dairy products and address the question of whether dairy fat itself is associated with an increased risk of IHD.

We agree that both biomarkers and dietary data have their own strengths and weakness in evaluating dietary intakes. Because biomarkers are free of reporting errors, we believe it is important to develop sensitive and specific biomarkers for nutrient or food intakes. Cumulative evidence suggests that 15:0 is a reasonable marker of dairy fat intake, although more validation studies are needed. Because dairy fat is only one component of dairy products, one cannot extrapolate results for 15:0 to health effects of dairy products, especially low-fat or non-fat dairy products that contain little or no 15:0.

ACKNOWLEDGMENTS

No conflicts of interest were reported.

REFERENCES

  1. Agriculture Research Service, US Department of Agriculture. USDA National Nutrient Database for Standard Reference—release 18 (2005). Washington, DC: US Department of Agriculture, 2006.
  2. Hu FB, Stampfer MJ, Manson JE, et al. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr 1999;70:1001–8.[Abstract/Free Full Text]
  3. Elwood PC, Pickering JE, Fehily AM, Hughes J, Ness AR. Milk drinking, ischemic heart disease and ischemic stroke I. Evidence from the Caerphilly cohort. Eur J Clin Nutr 2004;58:711–7.[Medline]
  4. Willett WC. Nutritional epidemiology. 2nd ed: New York, NY: Oxford University Press, 1998.
  5. Elwood PC, Strain JJ, Robson PJ, et al. Milk consumption, stroke, and heart attack risk: evidence from the Caerphilly cohort of older men. J Epidemiol Community Health 2005;59:502–5.[Abstract/Free Full Text]




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