Generated Summary
This review article assesses the role of dairy consumption in human nutrition and disease prevention. The authors investigate the recommended intake of milk products and the health benefits of a high intake, addressing concerns about potential adverse health outcomes. The article covers various aspects of dairy consumption, including the composition of dairy products, their effects on growth and development, bone health, fracture risk, body weight, obesity, blood pressure, cardiovascular disease, diabetes, cancer, allergies, and intolerances. It also touches on the environmental impacts of dairy production and the nutritional implications of organic and grass-fed production methods. The analysis includes data on milk consumption and hip fractures and also examines the role of dairy in relation to various health outcomes.
Key Findings & Statistics
- The recommended intake of milk or equivalent dairy products in the United States is three 8-oz (237 ml) servings per day for adults and children 9 years or older.
- The average intake among adults is 1.6 servings per day.
- Countries with the highest intakes of milk and calcium tend to have the highest rates of hip fractures.
- The estimated calcium intake needed to maintain balance was 741 mg per day.
- The estimated balance was attained at approximately 200 mg of dietary calcium per day among Peruvian men with low habitual calcium intake.
- Calcium supplements of 1000 to 2000 mg per day resulted in 1 to 3% greater bone mineral density than placebo in trials.
- In a meta-analysis of prospective studies, total calcium intakes ranging from less than 555 mg per day to more than 1100 mg per day were unrelated to the risk of hip fracture.
- Milk intake (ranging from fewer than 1.5 servings per week to 30 or more servings per week) or total dairy food consumption was unrelated to the risk of hip fracture in men or women in meta-analyses of prospective studies.
- In a meta-analysis of five trials with 6740 patients, no significant benefit from calcium was seen in reducing the number of all nonvertebral fractures (relative risk, 0.92; 95% CI, 0.81 to 1.05).
- The risk of hip fracture was greater among persons who received calcium supplements than those who received placebo (relative risk, 1.64; 95% CI, 1.02 to 2.64).
- The recommended daily allowance of calcium is 1000 mg per day for children 4 to 8 years of age, whereas in the United Kingdom 450 to 550 mg per day is considered adequate.
- Among girls in the early stages of puberty, calcium balance was positive even with an intake of less than 400 mg per day.
- In a 1976 study in the United Kingdom, 581 elementary-school children were randomly assigned to receive either school lunch with milk (about 7 oz, presumably of whole milk) or lunch without milk. After 21 months, no significant difference in weight was seen.
- In a meta-analysis of 29 randomized trials, no overall effects of milk or other dairy foods on body weight were seen.
- Studies of milk consumption and body weight in children are few, but among 12,829 adolescents followed for 3 years, intake of low-fat milk was positively associated with gain in body-mass index (BMI), but intakes of full-fat milk and dairy fat were not.
- Consumption of organic milk may have slightly higher amounts of n-3 polyunsaturated fatty acids and beta carotene than conventional milk.
- Dairy products consumption is strongly correlated with rates of breast cancer, prostate cancer, and other cancers.
- In a meta-analysis that included 29 cohort studies, intakes of milk (total, high-fat, and low-fat) or total intakes of dairy foods were not associated with overall mortality.
Other Important Findings
- The natural function of milk is to nourish and promote the growth of young mammals.
- Cows have been bred to produce higher levels of insulin-like growth factor I (IGF-I), and they are pregnant for most of the time they are milked, which greatly increases levels of progestins, estrogens, and other hormones in milk.
- Milk processing has many potential health implications, like pasteurization and fermentation which affect bacterial composition.
- If breast milk is not available, cow’s milk can add important nutritional value during early childhood.
- Cow’s milk contains substantial amounts of branched-chain amino acids leucine, isoleucine, and valine, which are key to protein quality.
- Tall stature is associated with lower risks of cardiovascular disease but with higher risks of many cancers, hip fractures, and pulmonary emboli.
- The health consequences of accelerated growth and greater adult height are complex.
- Consumption of these amino acids by humans increases plasma concentrations of IGF-I, which mediates growth hormone action.
- In a meta-analysis, total calcium intakes ranging from less than 555 mg per day to more than 1100 mg per day were unrelated to the risk of hip fracture.
- In a substitution analysis, the risk of diabetes was lower with milk consumption than with consumption of sugar-sweetened beverages or fruit juices but higher with milk consumption than with coffee consumption.
Limitations Noted in the Document
- Balance studies have limitations including short duration (2 to 3 weeks) and high habitual calcium intakes.
- Trials lasting 1 year or less can be misleading.
- The small size of balance studies and 2-to-3-week balance studies.
- The findings in the association of calcium supplements and fracture risk can be complicated to interpret because most supplements included both calcium and vitamin D.
- Studies examining calcium supplements are limited in size, number, and duration.
- The existing literature is that almost all prospective studies have been initiated among persons in midlife or later, whereas many cancer risk factors operate in childhood or early adult life.
- Studies of milk consumption and body weight in children are few and are subject to confounding and reverse causation.
- The reported health effects of dairy foods depend strongly on the specific foods or beverages to which they are compared.
Conclusion
The role of dairy consumption in human health and disease prevention requires careful assessment. While milk provides essential nutrients, including calcium and vitamin D, as well as multiple growth-promoting factors, all these nutrients can be obtained from other sources, especially in regions with low dairy consumption. The current recommendation to increase dairy intake is not justified for all individuals, particularly adults, due to the lack of clear evidence supporting its benefits for fracture reduction and weight management. Moreover, there are potential risks, such as increased risks of prostate cancer and possibly endometrial cancer. For children, milk may be a valuable substitute for mother’s milk. Milk intake promotes growth velocity and greater attained height, which presents both risks and benefits. Dairy’s high nutrient density can be advantageous in areas where diet quality is compromised, but caution is advised in high-income countries, where milk consumption has been associated with higher fracture risks and cancer concerns. In regions with low dairy consumption, alternative dietary sources such as kale, broccoli, tofu, nuts, beans, and fortified orange juice can provide sufficient calcium, while vitamin D supplements are a cost-effective option. The current guidelines could ideally designate an acceptable milk intake, emphasize whole milk over reduced-fat versions, and discourage the consumption of sugar-sweetened dairy products in populations with high rates of overweight and obesity. The environmental impacts of dairy production, especially industrial-scale production, contribute to greenhouse gas emissions, climate change, and water and pollution, as well as antibiotic resistance. The article emphasizes that health effects depend on specific dairy foods and their comparison, suggesting that dairy foods compare favorably with processed red meat and sugar-sweetened beverages, but less so with plant-based protein sources. The current recommendations to increase dairy consumption, particularly reduced-fat dairy, lack scientific support, and there is a need for further research to clarify the optimal milk intake based on diet quality and overall health outcomes.