Got Milk?

Abstract & Commentary

Synopsis: Dairy food intake is inversely associated with the risk of the insulin resistance syndrome.

Source: Pereira MA, et al. JAMA. 2002;287:2081-2089.

This paper is a product of the ongoing Coronary Artery Risk Development in Young Adults (CARDIA) Study, a prospective evaluation of more than 5000 people aged 18-30 years.1 At intake and at 7 years, questionnaires were used to collect information on diet, activity, cigarette smoking, demographics, and education. Pereira and colleagues included laborious detail on collection and assessment of dietary information. Milk, milk drinks, butter, cream, and cheeses made up about 90% of dairy intake in this sample. They also collected data on and control for other dietary factors such as whole grains, soft drinks, fish, and fruits. Physical measurements included height, weight, body mass index (BMI), waist to hip ration (WHR), and blood pressure. Laboratory data included fasting triglycerides, insulin, glucose, and HDL-C measurements. A total of 3157 participants were included in this analysis.

The insulin resistance syndrome (IRS) was defined as 2 or more of the following 4 components:

1. abnormal glucose homeostasis (fasting plasma insulin concentration of at least 20 micro units per milliliter, fasting glucose concentration of at least 110 mg/dL, or the use of medications to control blood glucose);

2. obesity (BMI of at least 30 kg/m2 or a WHR of at least 0.85 for women or 0.90 for men);

3. elevated blood pressure (at least 130/85 or the use of antihypertensives); or

4. dyslipidemia (HDL-C < 35 mg/dL or triglyceride > 200 mg/dL).

Dairy intake was higher in whites than in blacks, and lower in overweight individuals than in normal-weight individuals. Dairy consumption was positively associated with whole grain, fruit, vegetable, and saturated fat intake, and negatively associated with sugar-sweetened soft drink intake.

Incidence rates for IRS were higher for individuals who were overweight (BMI > 25 kg/m2) at baseline and for blacks. For overweight individuals, there was a consistent reduction in the incidence of each of the 4 components of the IRS with increasing intake of dairy products; there was a much weaker relationship between dairy intake and these findings in normal weight individuals. For overweight individuals, the odds ratio (OR) for IRS was strongly and inversely correlated with dairy intake, with an OR of 0.29 for those in the highest dairy intake category (35 or more servings per week), and 1.15 for those in the lowest dairy intake category (0-10 servings per week). This relationship was essentially unchanged by controlling for demographics, nondietary lifestyle factors, dietary fiber, and protein. This relationship seemed independent of whether the diary intake was high fat or low fat. Fiber and diary intake appeared to have a joint independent effect on reduction of IRS. Increasing dietary protein appeared to increase the incidence of IRS. In general, the odds of IRS were lowered about 21% for each daily eating of dairy products.

Comment by Barbara A. Phillips, MD, MSPH

When was the last time you had an overweight patient who walked in drinking milk? While this hardly ever happens, the number of obese individuals who blithely walk into my office carrying caffeinated, carbonated, sugar-filled, calorie-filled beverages in soda pop cans is astonishing.

Some prior evidence suggests that dairy products could have beneficial effects on weight control.2,3 It is possible that the lactose, fat, and protein in dairy products could affect satiety and perhaps reduce intake of calories in other forms (for example, soft drinks). Another possibility is that calcium or magnesium in dairy products could account for the findings presented here. Calcium and/or dairy intake may be associated with a decreased risk of cardiovascular disease.4-6 In the current study, however, Pereira et al found no meaningful change in the results when they controlled for intake of high carbohydrate foods or calcium.

The IRS, also known as the metabolic syndrome or syndrome X, is a constellation of risk factors that increases the risk of cardiovascular disease and diabetes. Its prevalence appears to be increasing, and this may account in part for the plateau of previously-declining cardiovascular disease rates.

It is notable that the increasing prevalence of IRS coincides with the increasing amount of soda ingestion by adolescents and young adults, while dairy product consumption (chiefly milk) has declined.7 Pereira et al conclude that ". . .increased dairy consumption may protect overweight individuals from the development of obesity and the IRS, which are key risk factors for type 2 diabetes and cardiovascular disease." My belief is that their recommendation, while supported by this study, will only work if individuals replace some intake (preferably soft drinks) with milk, rather than simply increasing total intake by adding milk on. With obesity, the basic problem remains one of taking in more calories than are being burned. 

Dr. Phillips, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington, KY, is Associate Editor of Internal Medicine Alert.

References

1. Friedman GD, et al. J Clin Epidemiol. 1988;41:1105-1116.

2. Carruth BR, Skinner J. Int J Obes Relat Metab Disord. 2001;25:5559-5566.

3. Zemel M, et al. FASEB J. 2000;14:1132-1138.

4. Ascherio A, et al. Hypertension. 1996;27:1065-1072.

5. Bostick RM, et al. Am J Epidemiol. 1999;149:151-161.

6. Abbott RD, et al. Stroke. 1996;27:813-818.

7. Cavadini C, Siega-Riz Am, Popkin BM. Arch Dis Child. 2000;83:18-24.