Author: Lee Jean
Institution: Integrative Biology
Date: September 2002
Erratum 7/26/16: Calcium content of milk corrected from 33-35 g to 33-35 mg.
This article is a collaborative effort between Jean Lee and Randy Wei (Integrative Biology, Molecular and Cell Biology, University of California at Berkeley).
From the "Got Milk" campaign to get people to drink more milk, to the "Not Milk" campaign decrying the benefits of milk, claims surrounding milk consumption are constantly debated. Milk producers advocate the benefits of calcium, vitamin D, and other nutrients, while detractors mention possible links to cancer or other diseases.
Milk is a familiar, one-of-a-kind beverage consumed by humans and other animals. But humans place themselves in the odd position of being the only animals that consume milk after weaning. Moreover, humans do not drink human milk, but drink the milk of other species, and do so commonly throughout their adult lives.
New alternatives to milk, such as calcium-enriched juices, soymilk, and rice milks, have stormed the markets. In Asian markets, powdered calcium is a popular commodity, often spooned into a pot of rice or soup. Milk and other dairy products are large parts of many diets around the world, but are they smart choices in our daily lives? To answer this, we need an increased awareness of this familiar yet ever-changing substance.
The Calcium Content of Milk
A large part of the ongoing milk advertisement campaign seeks to persuade people to drink milk for its calcium content. Indeed, calcium comprises a crucial aspect of human health. Not only is calcium needed for muscle contraction, but calcium lends to our bone structure, bone recovery (re-calcification), and bone health as well.
Human locomotion is made possible by rigid skeletons formed from calcium salts in the ground substance of bone. Less calcium therefore leads to weakened bones, resulting in the serious condition known as osteoporosis. Inappropriate levels of calcium can also lead to kidney stones, seizures, and body spasms. In addition, neurotransmitters specifically rely on calcium ions to continue to relay chemicals to areas of the body that need them. Lastly, calcium is an important factor in the blood coagulation cascade. In short, without calcium, humans could not survive.
The recommended daily allowance of calcium is approximately 800-1000 mg, although 1200 mg is ideal, according to the most recent update by the U.S. Food and Drug Administration (FDA). The FDA also notes that the majority of Americans consume only 500-700 mg per day, which is not enough. This leads to the debate about milk. Milk contains calcium, magnesium, zinc, proteins, fat, sugars, and vitamins A and D, what some call the "perfect package." However, the FDA reminds consumers not to capitalize on one source of nutrition. It recommends a variety of foods, the best choices being grains and vegetable sources.
According to a list proposed by the "Not Milk" campaign, milk contains less calcium per given amount than other foods. Raw turnip greens or cooked turnips, watercress, and seeds (such as sunflower or sesame) all contain larger amounts of calcium compared to milk. Compare the 234 mg of calcium in a 100-gram portion of almonds to the surprisingly low value of 33-35 mg of calcium per 100-gram portion in a typical milk sample (2% milk fat) from the store.
About 35% of one serving of milk (typically 240 mL) is calcium, which is a significant portion of the serving, but relatively calcium-poor when compared to most other sources of calcium, especially green leafy vegetables and grains. Milk still has more calcium per glass than some calcium-enriched juices, yet the calcium benefit of milk is still debated.
Unfortunately, milk and milk products cause an estimated 50% of the adult population's uncomfortable bloating, gas, cramping and diarrhea. Lactose intolerance can result from two things: either through a natural enzyme deficiency, which prevents the body from digesting milk sugars, or through an allergy to milk itself. The amount of lactase, the intestinal enzyme responsible for the digestion of lactose, the sugar found in milk, typically declines naturally after weaning, unless the body is genetically predisposed to produce more lactase.
After this decline, the disaccharide lactose cannot be broken down. Continued avoidance of lactose can send a signal to the intestinal brush border that lactase is no longer "needed" for activity, and decline can go further into completion than if the intestines were fed milk more often. But again, the natural tendency for the majority of world adult populations is the gradual lessening of enzyme activity.
One solution to the discomfort of lactose intolerance can be the consumption of dairy products pre-digested by lactase. Another simple solution is to take milk and dairy items out of the diet. Extensive cookbooks, such as The Milk-Free Diet Cookbook: Cooking for the Lactose Intolerant, are available for the lactose-intolerant. Other animal milks, such as the sweeter goat's milk, contain lower levels of lactose, making them easier to digest.
What risks come with drinking milk from cows injected with recombinant Bovine Growth Hormone (rBGH)?
When Ben and Jerry's Ice Cream decided not to use milk from cows injected with Monsanto's rBGH, many consumers became more conscious of what was in their food and milk products. Many dairy producers use rBGH as a way to increase milk production in their cows, resulting in up to 20% more production. However, the hormone causes udder inflammation in cows, which can lead to the contamination of the milk from secreted pus common in udder inflammation.
Also, antibiotics used to treat inflammation have been discovered in trace amounts in the milk. Such contamination leads many people to wonder whether milk is safe for daily human consumption.
In addition, milk produced by rBGH-treated cows has higher concentrations of insulin-like growth-factor-1 (IGF-1). Higher levels of IGF-1 have been indicated as a potential risk factor in prostate cancer.
In 1998, Harvard School of Public Health and Brigham and Women's Hospital reported in Science that men with IGF-1 levels in the highest quartile of study participants were 4.3% more likely to develop prostate cancer, compared to men with IGF-1 levels in the lowest quartile. Such a small increase in prostate cancer risk may or may not deter people from consuming milk from cows treated with rBGH.
Will I get kidney stones from drinking too much milk?
Many people drink a glass of milk daily for calcium and other essential minerals vital for healthy bones. Contrary to popular belief, milk does not lead to the formation of urinary stones or buildup of mineral deposits in the kidney. At the University of Chicago, D.R. Webb showed that even calcium-sensitive patients were able to consume milk or calcium-fortified orange juice without increasing their risk of stone formation. Patients drinking 600 mg of calcium in beverage form developed no kidney stones.
Milk plays an important role in many diets today. Many of us grew up eating cheese pizza, yogurt, milk and cookies, and cheesecake. We have grown so comfortable consuming milk and eating milk products that many do not give a second thought to the possible positive and negative effects of milk. Overall, milk does do a body good.
The negative side effects of milk are due mainly to the over-consumption of milk products beyond the recommended daily allowance of 3 8-oz glasses of milk. Consumers must be aware of both the pros and cons of drinking milk. Being knowledgeable consumers will empower us to decide how much we should rely on milk for our nutritional needs and empower us to be more proactive in creating a well-balanced and nutritious meal
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