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Drinking Milk Builds Strong Bones - Think Again...
Epidemiological studies show that countries with the highest milk consumption also have the highest rates of osteoporosis. This ironic observation makes the common belief that milk is required for strengthening bones questionable. However, the evidence that refutes the milk-for-stronger bones claim is actually solid. How can milk be bad for your bones? Are other dairy products also bad? If not milk, how else can you meet your daily recommended calcium intake? Read on to find out.
Milk is the primary source of nutrients for the young mammals. It is produced from the mammary glands and the composition of milk differs from one species to another.
For example, although cow milk and human milk mostly share the same nutrients, they are found in different amounts. While cow milk is made up of 3.4% protein, 3.6% fat and 4.6% lactose, human milk contains much less protein (1.1%), much more sugar (7% lactose) and about the same level of fat (4.2%).
Even though the milks of other domesticated mammals can be consumed, humans mostly consume cow milk.
While raw cow milk in its natural form is desirable, advances in hygiene technology created the process of pasteurization to remove harmful bacteria from milk. Currently, pasteurized milk is consumed more than raw, unpasteurized milk.
Besides protein, fat and lactose, milk also contains amino acids, water, vitamins A, D, B1, B2 and B12 as well as calcium, potassium, magnesium and sodium.
Fortified milk can also contain biotin, iodine, vitamin K and/or selenium.
Milk is commonly recommended for its high calcium content. However, milk is not the only dietary source of calcium. Green, leafy vegetables are also rich in calcium. However, vegetables such as kale and broccoli are better sources than others like spinach.
Vegetables belonging to the latter group contains antinutrients (phytates and oxalates) that can bind calcium and reduce its bioavailability.
To increase milk production in cows, the animals are given synthetic growth hormone. Cows naturally make their own bovine growth hormone (BGH) but milk production can be dramatically increased by administering rBGH (recombinant bovine growth hormone).
This synthetic growth hormone is produced from genetically engineered bacteria (E. coli). This may be responsible for the increased udder infection reported in cows given this synthetic hormone.
In addition, rBGH stimulates the release of insulin-like growth factor (IGF-1) from the liver.
Therefore, milk obtained from cows raised with rBGH may have significant levels of bovine growth hormone and insulin-like growth factor.
Concern over the negative effects of these hormones on human health is the reason why countries in the European Union as well as Australia, New Zealand, Japan and Canada banned milk obtained from cows treated with rBGH.
Unfortunately, the FDA (Food and Drug Administration) fully endorses such cow milk in the US.
There is an ongoing debate over the effect of milk on our bones. While some health experts insist that milk consumption is essential for healthy bones, others contend that milk consumption is actually bad for the bones.
It is worth noting, however, that humans are the only species that regularly consume the milk of other mammals.
In addition, only humans consume milk even after their formative years of rapid development.
Some health experts argue that cow milk is only good for the early years of development but some insist that consuming milk even in childhood can increase the risk of bone fractures later in life.
So, what are the pros and cons of milk consumption and how are the bones affected?
In the US, the official dietary guidelines recommend that adults should consume 3 glasses of fat-free or low-fat milk every day. This recommendation is given because milk is a ready source of calcium and vitamin D.
While the chief reason for recommending milk is to help develop stronger bones, studies have shown that there may be other constituents of milk that may provide other benefits.
For example, the linolenic acid found in milk and dairy products is believed to help reduce the risks of atherosclerosis, hypertension and certain cancers. In addition, trans-palmitoleic acid, a dairy fat, shows promise for lowering the risk of type 2 diabetes.
However, the link between calcium and bones is still the main reason why milk is recommended.
The most abundant mineral in the bone is calcium. When calcium is lost from the bones, they weaken and the risk of fracture is raised. Therefore, it follows that calcium supplementation should help keep the bones mineralized and strengthened.
However, recent evidences suggest that such a simple view of the link between calcium and bone health is inaccurate.
For one, the calcium obtained from diet and supplements only serve to raise blood calcium levels. Unfortunately, when calcium accumulates in the blood it can cause more harm than good.
High blood calcium levels lead to the calcification of major organs and soft tissues but especially the arteries and muscles. This can quickly worsen cardiovascular health, promote the formation of kidney stones and cause diseases affecting the muscle. Therefore, there is a need to drive the calcium in the blood into the bones.
To move calcium from the blood to the bones, the body needs 2 vitamins: vitamin D and vitamin K.
Because vitamin D is also found in milk, milk can potentially increase the amount of calcium bound to bone cells and, therefore, promote the mineralization of the bones.
Even then, the idea that only calcium and vitamin D are the active nutrients in milk is naïve.
Studies show that vitamin K plays a more prominent role than vitamin D in transporting calcium from the blood to the bones.
Furthermore, the protein content of milk is of particular importance because high protein diets exert a rather peculiar effect on the bones.
Dietary proteins, especially animal proteins, raise the body’s acidity levels. And milk protein is an example of animal proteins that can acidify the body.
Animal proteins are known to have positive PRAL (potential renal acid load) values. In response to the increasing acidity levels, the body tries to neutralize the acidity with alkalinizing agents before the acidic proteins reach the kidneys.
Unfortunately, calcium is one of the major alkalinizing substances used by the body to counter rising acidity.
Since bones are the richest stores of calcium in the body, the mineral is stripped from bones to quickly neutralize the acidic proteins coursing through the body. Therefore, the body recruits calcium to bind to acidifying animal proteins and guide them out of the body.
This means that calcium is excreted along with animal proteins and the bone experiences a net calcium loss.
Therefore, even though milk is an excellent source of calcium, its high protein content also makes it a chief cause of calcium loss in the body.
Perhaps the balance between the calcium and protein content of milk is the reason why human milk contains about one-third the protein content of cow milk. Therefore, our regular consumption of cow milk and some other dairy products increases the amount of acidifying animal proteins in the body and reduces the calcium content of the bones.
The processes involved in the production of milk such as pasteurization and homogenization can also increase the acidity of milk. Therefore, pasteurized milk is an even worse acidifier than raw milk.
Milk may be acidifying but not all dairy products are. In fact, cultured dairy products, especially unsweetened fermented milk products, are neither acidic nor alkaline.
Examples of acid-neutral dairy products include kefir and yoghurt. These milk products not only contain calcium but they are rich in other nutrients and probiotics.
For cooking and other types of food preparation, milk can also be replaced by healthier substitutes that have similar “look and feel”. Almond milk is a good milk alternative and it is an alkalinizing food rather than acidifying agent. Therefore, it will promote the retention of calcium in your bones.
Rice milk and organic soy milk are also good alternatives to cow milk.
You can also get your daily calcium requirement from other sources beside milk. While milk may be bad for your bones, calcium is absolutely essential. Therefore, you should consider other sources of calcium such as green leafy vegetables and calcium-fortified foods.
Vegetables such as kale, sprouts and broccoli are excellent foods for strengthening your bones because they also contain vitamin K.
Therefore, they contain readily available calcium (because they have low levels of oxalate, an antinutrient that chelates calcium and prevents it from being bioavailable) and vitamin K to move it from the blood into the bones.
Vitamin D is also an excellent vitamin to combine with calcium and vitamin K to improve bone health.
Lastly, and perhaps more importantly, regular exercise is essential for strengthening the bone. Some experts even believe that exercises are more important to bone strength than calcium.
This is because while calcium can increase your bone mineral density, that does not immediately translate to stronger bones. It is regular exercises that strengthen the core of the bone. In fact, you get 98% of your bone mass before you turn 20.
Therefore, the teenage years are the best time to strengthen your bones with exercise and not with milk.
A thorough examination of past studies shows that there are more studies to indicate that milk consumption is bad for the bones than there are positive studies. Most of the positive studies do not even specifically find milk useful.
A 2006 study published in the Journal of Bone and Mineral Research investigated the benefits of calcium and vitamin D3-fortified milk for reducing the risk of bone fractures in elderly men.
For this study, the researchers recruited 167 men over the age of 50. Over a period of 2 years, half of the group received 400 ml/day of low-fat milk containing 1,000 mg of calcium and 800 IU of vitamin D3. The results of the study showed that the milk group had higher serum vitamin D levels and higher bone mass density than the control group.
The researchers, therefore, concluded that calcium and vitamin D3-enriched milk can help slow down age-related bone loss and reduce the risk of fracture in the elderly.
While this study suggests that milk supplementation helps the bones, it is worth noting that the researchers used a specific formulation of milk. The milk used in this study had very high calcium and vitamin D3 levels.
Vitamin D3 is the specific vitamer of vitamin D that improves bone health.
In addition, the milk used was low-fat and subjected to ultra-high temperature that would have destroyed some of its proteins and left-over cow hormones.
Therefore, this study did not specifically prove that commercially available milk can prevent bone loss. It proved that that calcium and vitamin D-fortified and protein-denatured milk can improve bone mineralization.
A 2002 study published in The American Journal of Clinical Nutrition also found that children who avoided drinking cow milk had poor bone health.
However, what the researchers actually linked to poor bone health was low dietary calcium intake. Although they simply equated milk consumption to dietary calcium intakes, there are other calcium sources for kids besides milk.
A 1997 study published in the American Journal of Public Health determined whether higher intake of milk during adult years can reduce the risk of osteoporotic fractures.
For the study, the researchers gathered data from over 77,000 adult women over a period of 12 years. None of these women took calcium supplement.
With such big study population, the researchers were able to conclusively measure the effect of milk consumption on the risk of bone fractures. Their results showed that milk consumption (or indeed any dietary source of calcium) during adult years did not protect against bone fractures.
A 2012 study published in JAMA Pediatrics also arrived at the same conclusion. Here, the researchers recruited 6,712 adolescent girls all over the United States for the Growing Up Today Study.
The dietary intakes of calcium, dairy products and vitamin D were assessed with questionnaires every 1 – 2 years between 1996 and 2001. The dietary data gathered was then correlated with the incidence of fractures in the study population between 1997 and 2004.
The results of the study showed that calcium and dairy intakes did not affect the risk of stress fracture but vitamin D consumption significantly lowered this risk.
While these studies showed that milk consumption did not improve bone health, there are others that concluded that milk consumption can actually increase the risk of fractures.
One such study was published in the American Journal of Epidemiology in 1994. The authors of the study concluded that the consumption of dairy products up to age 20 years was linked to higher risk of hip fractures later in life.
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