Milk and Osteoporosis — Is Dairy Really Good for Your Bones?
But this new study found that drinking large amounts of milk did not protect men or women from bone fractures, and was linked to an overall higher risk of death during the study period.
Osteoporosis affects women twice as often as men. Additionally, it is estimated that 0.3 million and 1.7 million people have hip fractures in the USA and Europe, respectively. Having a proper peak bone mass and keeping it as long as possible is especially important for osteoporosis prevention. One of the most important calcium sources is milk and dairy products. Breast milk is the best infant food, but milk should not be avoided later in life to prevent losing bone mass. On the other hand, more and more people limit their milk consumption and consume other dairy or non-dairy products. For example, they are usually replaced with plant beverages, which should be consumed carefully in several age groups. Additionally, an important element of milk and dairy products, as well as plant beverages, are probiotics and prebiotics, which may modulate bone turnover. Dietary recommendations focused on milk, and dairy products are an important element for the prevention of osteoporosis.
However, the researchers said the results should be viewed with caution.
Women who drank three glasses of milk or more every day had a nearly doubled risk of death and , and a 44 percent increased risk of cancer compared to women who drank less than one glass per day, the researchers found.
Still, the findings only suggest an association and not a direct link, said Mary Schooling, a professor at the City University of New York School of Public Health, who wrote an editorial accompanying the study.
People should not change their diet based on these findings, Schooling said.
“We can’t draw conclusions at this point,” she said. “We need a study involving people who genetically can and can’t digest milk easily, and compare whether those who can digest milk have a difference in cardiovascular disease, death and fractures from those who can’t.”
The study involved more than 61,000 women and 45,000 men in Sweden who previously filled out dietary questionnaires for other research projects, the women in the late 1980s and the men in 1997. All were over 39 years of age.
Researchers compared their reported milk-drinking habits to health data kept by Swedish officials, to see whether milk consumption could be linked to risk of death or health problems.
In addition, excessive milk drinking appeared to actually increase a woman’s risk of broken bones, compared with women who drank little milk.
The risk of any bone fracture increased 16 percent in women who drank three or more glasses daily, and the risk of a broken hip increased 60 percent, the findings indicated.
Lots of milk did not appear to either protect against or promote broken bones in men.
Michaelsson and his colleagues said the increased risk of death they observed could be explained by the high levels of sugars contained in milk, specifically lactose and galactose.
Galactose has been shown to prematurely age mice in the laboratory, Michaelsson said, noting that the milk sugar promotes inflammation.
While interesting, these findings are too preliminary to warrant a change in nutritional guidelines, said Isabel Maples, a registered dietitian in Haymarket, Va., and spokesperson for the Academy of Nutrition and Dietetics.
About 55 percent of older adults — 44 million Americans — either have osteoporosis or are at high risk for brittle bones, Maples said. She added that the U.S. Dietary Guidelines recommend three servings of dairy per day, not just for bone health, but also to reduce the risk of heart disease, type 2 diabetes and high blood pressure.
“They don’t base the guidelines on fads. They don’t base it on trends. They don’t base it on what has been the traditional advice. They look at the scientific evidence,” she said.
Efforts by HealthDay to reach the National Dairy Council for comment on the study were unsuccessful.
“The countries with the highest rates of osteoporosis are the ones where people drink the most milk and have the most calcium in their diets. The connection between calcium consumption and bone health is actually very weak, and the connection between dairy consumption and bone health is almost non-existent.”
– Amy Lanou Ph.D., nutrition director for the Physicians Committee for Responsible Medicine in Washington, D.C.
The Milk Myth
For years we have been brought up with the belief milk is a good source of calcium and that drinking it promotes the development of strong teeth and bones. However, research undertaken by a team of Swedish scientists shows a link between milk consumption with increased mortality, bone fractures and osteoporosis.
In women over 20 years, drinking more than 200g of milk daily (less than one glass) was linked to increased mortality. This increased risk ranged from 21% for one to two glasses to 93% for those consuming three or more. More than one glass a day was also linked to an increased risk of fractures in women.
Other scientific studies about milk and osteoporosis contradict the conventional wisdom that dairy consumption helps reduce osteoporotic fractures. Surprisingly, studies demonstrating that milk and dairy products actually fail to protect bones from fractures outnumber studies that prove otherwise.
Cumming and Klineberg report that:
“Consumption of dairy products, particularly at age 20 years, was associated with an increased risk of hip fracture in old age. (“Case-Control Study of Risk Factors for Hip Fractures in the Elderly”. American Journal of Epidemiology. Vol. 139, No. 5, 1994).
Also a 12 year long Harvard Nurses’ Health Study found that those who consumed the most calcium from dairy foods broke more bones than those who rarely drank milk. This is a broad study based on 77,761 women aged between 34 and 59 years of age.
In the authors’ own words:
“Data does not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures.” (Source: Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. American Journal of Public Health. 1997).
Theory of Causality
Drinking excessive amounts of milk is believed to acidify the body’s natural blood pH, which in turn triggers a biological correction in order to protect the kidneys. As calcium is an alkaline mineral it is thought that the body sacrifices calcium from the bones to neutralise the rise in blood acidity. Calcium from the bones is then excreted in the urine and not recycled leaving a net calcium deficiency.
Milk also contains D-galactose, a type of sugar. Experimental evidence in animals has suggested D-galactose is associated with ageing and damage to tissues at a cellular level. Researchers say an injected dose of 100mg/kg of D-galactose has been shown to accelerate biological signs of ageing in mice, which is equivalent to 6 to 10g in humans, or the amount found in one to two glasses of milk.
Should we be drinking milk at all?
It may be unfair to label milk as the sole culprit for bone weakening. Calcium loss from the bones has been linked to high intakes of all animal protein, not just milk. By the age of 80, vegetarians tend to have lost less bone mineral compared to omnivores.
Research suggests that the more animal protein you eat, the higher your risk of hip fracture becomes. Cross-cultural studies show strong links between a high animal protein diet, bone degeneration, osteoporosis and the occurrence of hip fractures. In rural communities in China where most of the protein in the diet came from plant foods rather than animal foods, the fracture rate was one-fifth of that in the US.
All baby mammals start off drinking milk. A mother’s milk contains all the vitamins, nutrients and antibodies to give a baby the best start in life. However, as baby mammals grow they become intolerant to the lactose in milk and once weaned they never drink it again. Humans are the only exception within the mammal population that is able to consume milk into adulthood (although even some of us have a normal and natural lactose intolerance).
Also, each mammalian species has its own milk formula and cow’s milk is no exception. For example, cow’s milk contains on average three times the amount of protein than human milk, which is perfect for a baby bovine but arguably not so good for humans who require a different composition of nutrients.
Recommendation for Milk and Dairy Products in the Prevention and Treatment of Osteoporosis
Intake of milk and dairy products is beneficial for every age group but especially for children and adolescents, when the development of bone mass is dynamic. Milk and dairy products are sources of not only high bioavailability calcium but also of vitamin D and proteins. Patients with a lactose intolerance or cow’s milk allergy should avoid or limit milk and dairy product consumption.
Breast milk is an optimal food for infants. Children should be exclusively breastfed for the first six months of their life .
Human milk is also preferred food for children with a cow’s milk allergy.
Breastfeeding should be recommended for one-year-old children and higher as an element of the diet, if desired by the mother and child. However, it should be reminded that long breastfeeding may affect the BMD of a mother negatively.
Consumption of infant formula between 7 and 12 months of life results in a Ca:P ratio equal to 1.49:1, which complies with recommendations (1:1–1:2).
Homogenized, pasteurized milk (3.25% fat) may be introduced between 9 and 12 months of life. After 9–12 months, sheep’s milk fortified with vitamin D may be introduced as an alternative to cow’s milk.
One-year-old children should consume 500 mL (two cups) of milk daily.
Skimmed milk (1–2% of fat) may be introduced after the second year of life. According to the World Health Organization, semi-skimmed milk may be introduced after 12 months of life. Skimmed milk is not recommended for children aged less than 12 months because it does not contain essential fatty acids, fat-soluble vitamins, and high potential renal solute load in relation to energy .
Plant milk (soy, rice, almond and others) should not be introduced as an alternative to cow’s milk for children under two years of age.
Young child formulae are not necessary for children aged 1–3 years, but their implementation is one of the strategies used in order to increase intake of vitamin D, iron and omega-3 fatty acids, which are present in smaller quantities in cow’s milk .
Dairy products are a good source of calcium and other nutrients with high bioavailability. Three portions of dairy products may cover the daily need for calcium. According to the recommendation for the population of America, adults should consume three cup-equivalents of fat-free or low-fat (1%) dairy (including milk, yoghurt, cheese or fortified soy beverages) per day .
The elderly should not avoid milk and dairy products, because they are a source of high-availability protein, vitamin D, calcium, and phosphorus, which are important for preventing disorders occurring in the elderly, e.g., osteoporosis . It is vital to note that lactose intolerance is often common among older people, and for this group of patients, fermented dairy products (kefir, yoghurt) and lactose-free milk is the best choice.
It is vital to note that cow’s milk and plant beverages are various products, and plant milk cannot be considered as a fully valuable alternative to cow’s milk .
According to The National Osteoporosis Foundation, data about the impact of dairy products on bone are moderate.
Beneficial modification of gut microbiota due to the consumption of dairy products may increase calcium absorption and the production of short-chain fatty acids and serotonin, which affect bone metabolism directly.
Conclusions about Osteoporosis
So does milk cause osteoporosis? It is impossible to isolate milk protein as solely responsible for causing osteoporosis. There are many other lifestyle variables that may have an influence and need to be taken into consideration.
Many things affect bone health and osteoporosis including genetics, physical activity, body weight, smoking (including exposure to second hand smoke), alcohol consumption, hormone levels, and medications. Therefore, if any of those risk factors are more common in countries that have the highest dairy consumption, then the link between dairy and osteoporosis may be nothing more than a coincidence. However, these findings are interesting enough to make further studies into this topic viable, if not a priority