Higher dairy protein intake linked with infertility marker in some women

By Joan Stephenson

NEW YORK (Reuters Health) - Among infertile women, higher intake of protein from dairy products may be associated with a diminished capacity of the ovaries to produce good-quality egg cells, a new study suggests, though the finding is too tenuous to inform dietary advice to women seeking to conceive.

Although data from animal studies suggest that a low-protein diet may have an adverse effect on the number of ovarian follicles and ovarian reserve in adulthood, human data are lacking.

Diminished ovarian reserve is one of the major causes of female infertility. But the process leading to reproductive senescence “is currently poorly understood,” the study’s corresponding author, Dr. Irene Souter of the Massachusetts General Hospital (MGH) Fertility Center in Boston, told Reuters Health by email.

“Since women in western societies tend to conceive later in the reproductive years, the identification of factors (including diet) that affect the individual rates of reproductive aging might be of significant clinical value,” said Dr. Souter.

The study’s analysis of the relationship between the amount and source of dietary protein and ovarian reserve involved 265 women (mean age, 35) undergoing fertility treatment at MGH. These women were enrolled in the ongoing EARTH (Environment and Reproductive Health) study, a prospective cohort initiated in 2004 to evaluate effects of environmental factors on reproductive health.

Participants completed a questionnaire on how often they consumed specified amounts of foods, beverages, and supplements in the year before their enrollment in the study. A validation study found the correlation between the protein intake as assessed by the questionnaire and diet records prospectively collected for a year was 0.44, with much better recall for dairy foods than for vegetable-based proteins.

To evaluate ovarian reserve, participants also underwent ultrasonic determination of antral follicle count (AFC), a marker of ovarian primordial follicle numbers.

An analysis of the relationship between protein intake and AFC, adjusting for age, body mass index, race, smoking status and total energy intake, found that overall greater consumption of dairy protein comprising at least 5.24% of energy (2.3 cups of milk/day or more) was associated with lower AFC, the researchers report in BJOG, online March 9.

The mean AFC was 14.4% lower for women in the highest quintile of dairy protein intake (5.24% of energy or more) compared with women in the bottom quintile (2.31% of energy or less), after adjusting for potential confounders (p=0.009)

“We found no such association between protein derived either from vegetable or other non-dairy animal sources,” said Dr. Souter.

Because the study evaluated a population of women presenting for evaluation and treatment of infertility, its findings may not apply to a population of women who conceive spontaneously and should be “interpreted with caution,” she said.

“The presence of measurable amounts of steroid hormones and growth factors in dairy products, as well as the contamination of dairy products by pesticides and endocrine-disrupting chemicals, might be adversely affecting the health of the human ovary, potentially accelerating its aging,” Dr. Souter said.

The study’s findings “should be reproduced in prospective studies designed to also clarify the biology underlying the observed associations,” she said.

The new study “adds to the growing number of conflicting studies on the association between dairy intake and ovarian reserve,” said Dr. Lauren A. Wise, an epidemiologist at Boston University School of Public Health, who was not involved in the study, in an email to Reuters Health.

“Interpretation of the data was hampered by the lack of a dose-response relation between dairy protein intake and ovarian reserve,” with similar AFCs in the first through fourth quintiles of dairy protein intake, but much lower in the fifth quintile, said Dr. Wise, who leads the PRESTO (Pregnancy Study Online) project, which seeks to identify diet and other lifestyle factors that may affect fertility and pregnancy outcomes.

The researchers also obtained information about diet after the diagnosis of infertility, and the cause of infertility, such as ovulatory dysfunction, was known for more than half of participants at enrollment, she noted.

“If the diagnosis of infertility influenced a change in diet, the results could have been biased,” Dr. Wise cautioned. Prospective studies measuring dietary intake before the occurrence of infertility will be particularly important for confirming these results.

“At this time, I believe that it is premature for clinicians to be making any health recommendations about dairy intake to women who are planning a pregnancy,” she said.

The study had no commercial funding. One author is employed by Nestle Research Center.

SOURCE: http://bit.ly/2oz7eQv

BJOG 2017.

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