MILK and HEALTH – A Topic of Interest and Surprising Findings!

Milk and dairy products are major components of the Western diet, especially in cold climates. Drawing on research, this article discusses milk's composition, its effects on health and its relationship with disease.

A Brief Overview of the Nutritional Content of Dairy Products

Because milk's natural function is to promote growth and development, it contains all essential nutrients and multiple anabolic hormones.

To increase milk production, cows have been made to produce higher levels of insulin-like growth factor I (IGF-I). This has greatly increased the levels of progestin, estrogen and other hormones in milk.

Processing milk has many effects on health. Pasteurization reduces the transmission of brucellosis, tuberculosis and other pathogens. The fermentation needed to produce cheese, yogurt and kefir denatures milk's peptide hormones. It changes protein antigens, reduces lactose content and affects bacterial composition.

How Does Milk Affect Growth and Development?

Cow's milk can add substantial nutritional value to the diet in early childhood. However, normal growth and development throughout childhood can be achieved without dairy products. In diets containing few animal products, attention must be paid to diet quality, including the use of vitamin D and supplemental vitamin B12.

Milk consumption promotes growth, development and height. It is unclear whether this growth-promoting effect is due to specific amino acids, anabolic hormones or other factors.

Cow's milk contains the amino acids valine, leucine and isoleucine, which are key to its protein quality. Leucine specifically activates the rapamycin signaling pathway (mTOR), which promotes cell proliferation and suppresses apoptosis (programmed cell death). Consuming these amino acids increases blood levels of IGF-I, which mediates the effects of growth hormone.

However, the health consequences of accelerated growth and greater adult height are complex. Taller individuals have been associated with a higher risk of cardiovascular disease; taller patients with cancer also have a higher risk of hip fracture and pulmonary embolism.

How Does Milk Affect Bone Health and Fracture Risk?

The rationale behind drinking milk for longevity has been to meet calcium requirements for bone health. Paradoxically, however, countries with the highest milk and calcium intake tend to have the highest rates of hip fracture. This association may not be causal. It may be influenced by various factors, such as vitamin D deficiency and differences in ethnicity.

A study of 10,000 women and men in the USA found no association between calcium intake and bone mineral density at the hip.

A meta-analysis of prospective studies found no association between total calcium intakes of less than 550 mg and more than 1100 mg per day and hip fracture.

In a randomized trial, consuming 3 additional daily servings of milk or equivalent dairy products had no effect on bone mineralization in boys and girls in early puberty whose calcium intake was below 800 mg per day.

Available data linked each additional daily intake of milk during adolescence in males to a 9% higher risk of hip fracture later in life. The same association was not observed in females. Current data therefore do not support increased milk intake during adolescence to prevent hip fractures later in life.

In the United States, the recommended daily calcium intake for children aged 4-8 is 1000 mg. In the United Kingdom, 450 to 550 mg per day is considered sufficient. Whole UHT milk contains an average of 107 mg of calcium per 100 ml. Whole pasteurized milk contains 523 mg of calcium per 100 ml. Whole white cheese contains 422 mg of calcium per 100 grams.

Among girls in early puberty, calcium balance remains positive even at intakes below 400 mg per day. Among children aged 4-8, calcium intake has not shown a directly proportional relationship with bone mineral density. This weakens the evidence that additional calcium intake is necessary throughout childhood.

Although calcium's effects on bone mineral density are uncertain, a large cross-sectional study in the United States found that phosphorus intake was positively associated with bone mineral density. Whole white cheese contains an average of 282 mg of phosphorus.

The Effect of Milk Consumption on Weight and Obesity

Although milk consumption is widely believed to benefit weight control / weight loss, studies have found no overall effect of milk and dairy products on weight control. However, yogurt consumption has been considered protective against obesity. Yogurt is a naturally fermented food that contributes to the gut microbiota. The possibility that people who consume yogurt have healthy lifestyles cannot be ruled out.

A study that followed 12,829 adolescents for 3 years found that low-fat milk consumption resulted in weight gain and an increase in body mass index (BMI), but this effect was explained by high dietary energy intake rather than whether the milk was low-fat or whole.

In another study of milk consumption in young children, whole milk was associated with a lower rate of obesity than low-fat milk. A separate study found no association between milk consumption and body fat.

Taken together, the studies do not allow us to say that milk has an obesity-reducing effect.

Milk's Effects on Blood Pressure, Lipids and Cardiovascular Disease

Milk's relatively high potassium content has led to the suggestion that drinking more milk could lower blood pressure. The DASH diet, recommended for controlling hypertension, lowers blood pressure, but milk's specific contribution is uncertain because the diet is low in salt and rich in vegetables and fruit.

If milk replaces sugary drinks or other refined carbohydrates, the outcomes are likely to be beneficial. However, the outcomes may differ if it replaces hazelnuts, legumes or whole fruit.

In studies, full-fat and low-fat products had similar effects on coronary heart disease. Both were associated with a lower risk than an equal serving of red meat, but a higher risk than fish and nuts.

Current recommendations favor low-fat dairy products over full-fat sources to reduce the risk of heart disease.

Saturated fat (approximately 65% of milk fat is saturated) increases low-density lipoprotein cholesterol (LDL, bad cholesterol), and elevated LDL cholesterol is a risk factor for coronary heart disease. However, the reported effects of saturated fats vary depending on their source.

To better understand this, let us examine the study findings below.

Replacing most carbohydrates with saturated fat lowers LDL cholesterol (commonly known as bad cholesterol) and raises HDL cholesterol (commonly known as good cholesterol), but also increases triglycerides as an adverse effect.

Replacing saturated fat with unsaturated fats has similar benefits without an adverse effect on LDL cholesterol.

- Related Topic: What Should Cholesterol (HDL, LDL and Triglyceride) Levels Be by Age?

Whether milk is beneficial or harmful actually depends on what you consume instead of it. Consuming too much or too little of something may adversely affect health.

For people living in low-income countries whose diets are very high in starch, moderate dairy intake may reduce cardiovascular disease by providing nutritional value and lowering the glycemic load.

Milk's Effects on Diabetes

Cow's milk has been proposed as a cause of type-1 diabetes because of cross-reactivity between milk proteins and pancreatic islet cells, but this relationship remains uncertain.

Dairy intake has been associated in some cohort studies with a modestly lower risk of type-2 diabetes.

The Relationship Between Milk Consumption and Cancer

Dairy consumption has been associated with breast cancer, prostate cancer, endometrial (uterine) cancer and other cancers.

The mechanism underlying the increase in prostate and breast cancer risk with milk consumption may be explained by its effects on circulating insulin-like growth factor-I (IGF-I). In prospective cohort studies, milk consumption is most consistently associated with an increased risk of prostate cancer, particularly aggressive disease, but not with a higher risk of breast cancer.

Total milk intake has been associated with a greater risk of endometrial cancer, particularly in postmenopausal women not taking hormone therapy, a finding that may relate to the sex hormone content of dairy products. Dairy products or lactose have been hypothesized to increase ovarian cancer risk, but a comprehensive analysis found no association. By contrast, in meta-analyses and pooled analyses of primary data, milk consumption was inversely associated with colorectal (colon and rectal) cancer risk, potentially because of its high calcium content. An important limitation of the literature is that almost all prospective studies have begun in middle-aged or older people, whereas many cancer risk factors act during childhood or early adult life. A study of adolescent diets found that milk intake was unrelated to future breast cancer risk.

Various reports suggest that milk consumption may worsen allergic tendencies by predisposing people to asthma, eczema and food allergies.

Organic Milk

Organic milk has been promoted for its better nutritional composition. The use of recombinant growth hormone and the presence of pesticide and antibiotic residues in conventional milk also make organic milk more appealing. Organic milk may contain more omega-3, polyunsaturated fatty acids and beta-carotene than conventional milk. However, this is a consequence of the dairy animal being grass-fed rather than the milk being organic.

Conclusion

Cow's milk contains a complex combination of macronutrients, micronutrients and growth factors that can contribute to human nutrition. However, all these nutrients can be obtained from other sources, as is the case in many traditional societies with historically low dairy intake.

Taken together, the evidence does not support consuming large amounts of milk to reduce fracture risk. However, further research is needed into cow's milk's effects on children and the evidence suggesting that children should consume more milk for growth and development.

We can say that consuming large amounts of dairy products increases the risk of prostate, breast and endometrial cancer while reducing colorectal cancer risk. Across dairy products overall, no clear benefit of low-fat milk consumption has been observed.

In addition, total milk consumption has not been clearly associated with weight control, diabetes or cardiovascular disease risk.

Milk consumption may be beneficial in regions where diet and energy intake are inadequate. However, the recommendation to consume 3 or more daily servings of milk / dairy products does not seem justified. The optimal intake depends on a person's diet quality. It may help when diet quality is poor, but excessive intake may be harmful when diet quality is high.

A new factor increasing our daily milk consumption is milk-based coffee, which has become especially popular among young people. These coffees also contain substantial amounts of sugar, and this new habit is likely to have adverse long-term health effects.

What deficiencies may occur when milk consumption is reduced? Low milk intake raises concerns about deficiencies in two nutrients: calcium and vitamin D. These nutrients can be obtained from other sources without the potential concerns. Dietary calcium sources include cabbage, broccoli, tofu, hazelnuts, beans and fortified orange juice. Vitamin D supplements can provide adequate intake at a much lower cost than milk.

The recommended intake of milk and dairy products for adults is 0-2 servings per day.

Related Topic

8 Shared Traits of the World's Longest-Lived Blue Zone People

Best diets 2020