Is Milk a cause of Osteoporosis or Osteopenia?
IS MILK A CAUSE OF OSTEOPOROSIS? There have been a number of web sites and Internet postings claiming that Milk is the cause of Osteoporosis. Surprising news! Now let's look at the research.
The statement is backed up by two argument. First there is a claim that societies such as Mexico and Polynesia that traditionally do not use milk, have low rates of Osteoporosis but societies such as the United States and Sweden where milk is often consumed have high rates of Osteoporosis. This true. Mexico and Polynesia have lower incidence of Osteoporosis than the United States, Sweden and a number of other countries. These web site authors then conclude that Milk causes Osteoporosis.
The second argument says that Milk which has protien tends to acidify the body. Since your body needs to keep your blood at a stable acid/base ratio, base minerals such as calcium are pulled from bones and teeth to normalize the acid/base ration after drinking milk. Thus, they conclude, Milk is a cause of Osteoporosis.
So, let us exaine at these arguments.
It appears that the authors have forgottes some important things.
First, there is genetic inheritance. Every study related to body shape concludes the body type greatly affects the rate at which people develop Osteopenia and Osteoporosis. People of Mexico and Polynesia tend to be short and heavy boned while the United States and Sweden have many people born with long, thin bones. Inheritated body type should be included in any cross cultural statements about Osteoporosis.
Second,there is a geographical factor that those making these claims about Milk and Osteoporosis seem to ignore. Mexico and Polynesia are near the equator and so inhabitants are exposed to more sunlight inducing Vitamin D. Much of the United States and Sweden are above the 41st parallel and studies show that inhabitants do not get sufficient sun exposure during late Fall and winter for optimal Vitamin D production.
Third, there is a difference in life style that affects bone making. People in Mexico and Polynesia have been far less sedentary than those in the United States and Sweden. Not only do they walk more but many are employed in very physical jobs and their recreation is different. In Mexico, for example, Sunday aftenoons are likely to be filled with playing soccer or family walks outdoors rather than watching sports on T.V.
Also, it is not just a non-dairy diet typifies Mexico and Polynesia. Residents eat more fuits and vegetables, less soda pop and far less highly processed foods. So a scientific argument drawing comparisons between cultures needs to consider ALL relevant factors and not just pull one characterisitic and then claim it explains everything.
As for the acid/base arguement. There is much to support the notion that a highly acidic diet is a cause of bone loss. But milk is not just protein. It has carbohydrates and fats too. Also, most people do not just drink milk. Eating a peice of fruit with a glass of milk or drinking milk with a meal that includes fruit or salad, more than takes care of evening out the base/acid ratio. There is probably more damage done from drinking soda pop with its high phosophorous and caffeine content than could ever be done from a glass of milk.
And finally, there are a number of studies of adolescence that show that those who drink milk, tend to have greater bone density than those who do not. So, it appears that the recent rash of "milk causes of Osteoporosis" claims are very short on accurate scientific reasoning. I, for one, shall continue to eat yogurt, cheese, milk and other dairy products as a way to ensure I have enough calcium in my diet.
Research: Milk and Osteoporosis
Nutr Metab (Lond). Feb. 2006; "Determinants of bone mass and bone size in a large cohort of physically active young adult men". by JA Ruffing, F Cosman, M Zion, Susan Tendy , P Garrett, R Lindsay and JW Nievescorresponding author.
"The determinants of bone mineral density (BMD) at multiple sites were examined in a fit college population. Subjects were 755 males (mean age = 18.7 years) entering the United States Military Academy. A questionnaire assessed exercise frequency and milk, caffeine, and alcohol consumption and tobacco use. Academy staff measured height, weight, and fitness. Calcaneal BMD was measured by peripheral dual-energy x-ray absorptiometry (pDXA). Peripheral-quantitative computed tomography (pQCT) was used to measure tibial mineral content, circumference and cortical thickness. Spine and hip BMD were measured by DXA in a subset (n = 159).
Mean BMD at all sites was approximately one standard deviation above young normal (p < 0.05). African Americans had significantly higher hip, spine and heel BMD and greater tibial mineral content and cortical thickness than Caucasians and Asians. In Caucasians (n = 653), weight was a significant determinant of BMD at every skeletal site. Prior exercise levels and milk intake positively related to bone density and size, while caffeine had a negative impact. There was an apparent interaction between milk and exercise in BMD at the heel, spine, hip and tibial mineral content and cortical thickness. Our data confirm the importance of race, body size, milk intake and duration of weekly exercise as determinants of BMD and bone size.