Dairy and Fertility: An Evidence-Based Overview for Dietitians

Fertility is influenced by a combination of genetic, lifestyle, and dietary factors. Among modifiable factors, diet—particularly dairy intake—has received growing attention for its potential role in reproductive health. 

Dairy is a major source of nutrients such as calcium, vitamin D, protein, and fats, all of which play roles in hormonal balance, metabolic function, and overall health. However, research on dairy’s impact on fertility has produced mixed results. 

This article explores the biological mechanisms behind dairy’s influence on fertility, reviews key research findings, evaluates the strength of the evidence, and provides practical dietary recommendations.

Theories Linking Dairy and Fertility

Several theories have been proposed to explain the effects of dairy consumption on fertility:

Hormonal Content of Dairy

Dairy products naturally contain hormones, including estrogens and progesterone. Some researchers hypothesize that these exogenous hormones may disrupt endocrine function and affect ovulation​​. However, studies have not consistently shown a strong effect.

Fat Content and Ovulation

Observational studies suggest that the type of dairy consumed—high-fat versus low-fat—may have differing effects on fertility. High-fat dairy is associated with a reduced the risk of anovulatory infertility, while low-fat dairy has been linked to an increased risk. This difference may be due to how dairy fat affects hormonal balance and metabolism​​. However, it is important to note that not all studies find this association. 

Galactose Toxicity Hypothesis

Galactose, a sugar derived from lactose in dairy, has been shown in animal studies to impair ovarian function and induce ovarian toxicity. However, human studies have found no adverse effects​​.

Dairy’s effect on reproductive hormones 

There are theories that dairy intake may influence key reproductive hormones, including:

• Estradiol: Higher dairy intake has been associated with lower serum estradiol levels, which may have implications for reproductive health 

• Luteinizing Hormone (LH): High-fat dairy consumption in rodents has been linked to increased LH levels, which play a role in ovulation​.

• Testosterone and androgens: Some studies suggest that dairy consumption may impact androgen levels, which can be important in individuals living with Polycystic Ovarian Syndrome (PCOS)

Dairy, Insulin Sensitivity and PCOS

Dairy products are rich in calcium and vitamin D, both of which play a role in insulin regulation. Improved insulin sensitivity is particularly relevant for individuals with PCOS, a common cause of infertility. Studies suggest that moderate dairy intake, particularly full-fat dairy, may help regulate insulin levels and improve ovulatory function 

Evidence: Key Findings from Research

Research on dairy and fertility includes both observational and interventional studies.

High-Fat Dairy and Anovulatory Infertility

One of the most well-known studies examining dairy and fertility is the Nurses’ Health Study (NHS), which tracked the dietary patterns and fertility outcomes of 18,555 women over several years. The study found that:

• Women who consumed at least one serving of high-fat dairy per day had a 27% lower risk of anovulatory infertility compared to those who consumed low-fat dairy

• Conversely, low-fat dairy intake was associated with an increased risk of anovulatory infertility, suggesting that the removal of fat from dairy may alter its impact on reproductive hormones​

Later studies have found mixed results on the impact of dairy and fertility.

Dairy and IVF Outcomes

The Environment and Reproductive Health (EARTH) Study, a prospective cohort study involving 232 women undergoing 353 IVF treatment cycles, investigated the role of dairy intake on assisted reproductive technology (ART) outcomes. Key findings included:

• Women who consumed more than 3 servings of dairy per day had a 55% higher live birth rate compared to those consuming less than 1.34 servings per day

• The beneficial effect was only observed in women aged 35 years or older, indicating that dairy may be particularly important for older individuals undergoing fertility treatments

• There was no significant association between dairy intake and intermediate outcomes such as endometrial thickness, oocyte yield, or embryo quality​​

Dairy and General Fertility Trends

Findings from large-scale preconception cohort studies such as Snart Foraeldre (Denmark) and PRESTO (North America) have provided mixed results regarding the impact of dairy on natural fertility:

• The Snart Foraeldre study, which included over 2,400 women in Denmark, found that:

  • Women who consumed ≥18 servings of dairy per week had a 37% higher fecundability ratio (likelihood of conception per menstrual cycle) compared to those consuming fewer than 7 servings per week

  • This positive association was primarily driven by milk consumption and observed only in women under 30 years of age​

• The PRESTO study, conducted in North America, followed 1,300 women attempting to conceive and found no clear association between dairy intake and fertility.

  • This discrepancy suggests that cultural dietary differences, dairy processing methods, and genetic factors may influence dairy’s impact on fertility​.

Dairy and Polycystic Ovary Syndrome (PCOS)

PCOS is a common cause of infertility, characterized by hormonal imbalances, insulin resistance, and irregular ovulation. Dairy’s potential role in improving insulin sensitivity has led researchers to examine its impact on fertility in individuals with PCOS.

One review reported that: 

• High-fat dairy intake was associated with higher luteinizing hormone (LH) levels, which play a key role in ovulation

• Women who consumed more than one serving of yogurt or cream per day had a higher risk of sporadic anovulation, suggesting that certain types of dairy may have different effects on ovulation​ (though this has not been found in other studies)

• Calcium and vitamin D-rich dairy products improved menstrual cycle regularity

• Fermented dairy (e.g., kefir and probiotic yogurt) was associated with lower levels of inflammation and improved insulin sensitivity, which may help restore ovulation in individuals with PCOS​

Quality of the Evidence

The evidence on dairy and fertility varies in quality and consistency. Key considerations include:

1. Type of Studies:

   • Most studies are observational, meaning they can identify associations but cannot establish causality

     
     

2. Potential Confounding Factors:

   • Many studies adjust for factors like BMI, age, and lifestyle, but residual confounding is always possible.

   • Variations in dietary patterns, genetic differences, and environmental exposures may contribute to differences in findings​

     
     

3. Mechanistic Uncertainty:

   • While some biological mechanisms have been proposed, the exact pathways through which dairy affects fertility remain unclear

   • Some findings may be due to dairy’s nutrient composition rather than dairy itself, making it difficult to isolate specific effects​

Key Takeaway for Dietitians

Research on dairy and fertility shows inconsistent results, with some studies suggesting high-fat dairy may be beneficial for ovulation and pregnancy outcomes, while others find no strong link. Dairy intake does not appear to harm fertility, and moderate consumption, particularly of full-fat dairy, may be a better choice for those trying to conceive. However, more high quality research and randomized control trials are needed to better understand the effects of diary on fertility