March 21, 2013

Dairy products and fertility: does milk help or harm?

I believe that the verdict is quiet clear that dairy may have negative effects on health.
Dairy is full of saturated fat and is linked to heart disease. Dairy causes digestive problems for the 75 percent of people with lactose intolerance. Dairy aggravates allergies and increases mucous production.

The only very large study looking at dairy and fertility was published in 2007 by the Harvard University group that ran the very large "Nurses' Health Study".  This is a perspective study  started in 1989 when more than 116 000 female registered nurses aged 24–42 completed and returned a mailed baseline questionnaire. Participants have been followed every 2 years since then with mailed questionnaires, including information on exposures and disease outcomes.

The objective of the study was to find if there was a link between milk consumption and ovulation anomalies. the conclusion of the study was that High intake of low-fat dairy foods may increase the risk of anovulatory infertility whereas intake of high-fat dairy foods may decrease this risk.

The study also concluded that  lactose  does not significantly impairs ovulatory function to the point of affecting fertility.

These findings go in what the authors describe as :  "opposite directions for low-fat and high-fat dairy foods and the fact that the strength of the associations did not seem to depend on the lactose content of the food"

I believe that   this is a typical example of a useless study that  end up with spurious otcomes due to the fact that people who have awareness of a health problem change their habits accordingly : in this case women with polycystic ovaries who had ovulatory problems tried to consume low-fat products believing that they are healthier.

A similar finding happened for a recent study in which obese children were more likely to consume low-fat milk. Its sort of the "chicken and the egg story".

The bottom line is that dairy may affect fertility at an immunological level, not only ovulatory. Based on this study the authors themselves did not feel confortable endorsing the consumption of milk by women who are trying to get pregnant or have infertility.

Abstract below:

Dairy foods and lactose may impair fertility by affecting ovulatory function. Yet, few studies have been conducted in humans and their results are inconsistent. We evaluated whether intake of dairy foods was associated with anovulatory infertility and whether this association differed according to fat content.
METHODS We prospectively followed 18 555 married, premenopausal women without a history of infertility who attempted a pregnancy or became pregnant during an 8-year period. Diet was assessed twice during the study using food—frequency questionnaires
RESULTS During follow-up, 438 women reported infertility due to an ovulatory disorder. The multivariate-adjusted relative risks (RR) [95% confidence interval (CI); P, trend] of anovulatory infertility comparing women consuming ≥ 2 servings per day to women consuming ≤1 serving per week was 1.85 (1.24–2.77; 0.002) for low-fat dairy foods. The RR (95% CI; P, trend) comparing women consuming ≥ 1 serving per day of high-fat dairy foods to those consuming ≤1 serving per week was 0.73 (0.52–1.01; 0.01). There was an inverse association between dairy fat intake and anovulatory infertility (P, trend = 0.05). Intakes of lactose, calcium, phosphorus and vitamin D were unrelated to anovulatory infertility.
CONCLUSIONS High intake of low-fat dairy foods may increase the risk of anovulatory infertility whereas intake of high-fat dairy foods may decrease this risk. Further, lactose (the main carbohydrate in milk and dairy products) may not affect fertility within the usual range of intake levels in humans. 
  1. Hum. Reprod. 22 (5): 1340-1347. doi: 10.1093/humrep/dem019

1 comment:

  1. Such a nice and informative article. Glad to know about this study Method, Results and conclusion. A useful one for me. Thanks a lot for sharing.