Milk causes cancer: is this true, what is the real risk?
Recently a friend told me that drinking milk greatly increased one's risk of getting cancer and was insistent that drinking milk was it was a very serious health risk. I should note that my friend is a vegan (a vegetarian that eats NO animal products whatsoever - not even honey) and I am a practicing omnivore (one who eats both plants and animals) like most people. As one could guess, we had a very lively discussion.
To find the truth in this matter, one must do some serious digging to weed out the hype and to put things into perspective. As part of my research into this issue I decided to rely upon the following sources: government websites where there was absolutely no chance of bias (e.g. I did not rely upon anything from the U.S. Department of Agriculture as it might be biased towards the dairy industry); peer reviewed scientific papers; and reports by highly respected scientific journals that referenced peer reviewed research (e.g. American Journal of Epidemiology). What I learned was very interesting and I thought I would share it here.
Before I get to the issue of milk, I first want to provide overall cancer rates and briefly cover what is one of the most significant causes of cancer that few take seriously. The goal with this brief "side trip" is to help bring this whole issue into perspective.
Cancer rates in the U.S. (CDC 2003)
NOTE: When scientists look at cancer risks, they typically look at the number of incidents per 100,000 persons. For instance, at a cancer rate of 406.7 per 100,000, 0.4067% of the population would have contracted cancer. Put another way, the risk of getting cancer would be around 1 in 246.
- All cancers combined:
- White: 406.7 (or 0.4067%), mortality rate: 159.7
- Black: 379.1 (or 0.3791%), mortality rate: 188.2
- Hispanic: 316.8 (or 0.3168%), mortality rate 106.3
- Asians/Pacific Islander: 263.9 (or 0.2639%), mortality rate 97.3
- American Indians/Alaska Native: 247.7 (or 0.3074%), mortality rate 106.8
- Whites: 530.9 (or 0.5309%), mortality rate: 230.6
- Black: 611.0 (or 0.611%), mortality rate: 311.4
- Hispanic: 421.1 (or 0.4211%), mortality rate 158.1
- Asians/Pacific Islander: 329.3 (or 0.3293%), mortality rate 138.4
- American Indians/Alaska Native: 307.4 (or 0.3074%), mortality rate 142.3
- Most common forms of cancer :
NOTE: these are diagnosis rates not mortality rates.
- White: 1) Breast cancer: 119.0 per (or 0.119%); 2) Lung cancer: 55.7 (or 0.0557%); 3) Colorectal cancer: 43.0 per (or 0.043%)
- Black: 1) Breast cancer: 119.0 per (or 0.119%); 2) Colorectal cancer: 52.5 per (or 0.0527%); 3) Lung cancer: 50.4 per (or 0.0504%)
- Hispanic: 1) Breast cancer: 119.0 (or 0.119%); 2) Colorectal cancer: 34.7 (or 0.0347%); 3) Lung cancer: 26.2 (or 0.0262%)
- Asian/Pacific Islander: 1) Breast cancer: 119.0 (or 0.119%); 2) Colorectal cancer: 31.2 (or 0.0312%); 3) Lung cancer: 26.2 (or 0.0262%)
- American Indian/Alaska Native: 1) Breast cancer: 119.0 (or 0.119%); 2) Lung cancer: 36.8 (or 0.0368%); 3) Colorectal cancer: 33.4 (or 0.0334%)
- White: 1) Prostate cancer: 150.0 (or 0.150%); 2) Lung cancer: 85.8 (or 0.0858%); 3) Colorectal cancer: 59.2 (or 0.0582%)
- Black: 1) Prostate cancer: 150.0 (or 0.150%); 2) Lung cancer: 106.1 (or 0.1061%); 3) Colorectal cancer: 69.4 (or 0.0694%)
- Hispanic: 1) Prostate cancer: 150.0 (or 0.150%); 2) Colorectal cancer: 49.3 (or 0.0493%); 3) Lung cancer: 48.6 (or 0.0486%)
- Asians/Pacific Islander: 1) Prostate cancer: 150.0 (or 0.150%); 2) Liver cancer: 15.6 (or 0.0156%); 3) Colorectal cancer: 14.0 (or 0.014%)
- American Indian/Alaska Native: 1) Prostate cancer: 150.0 (or 0.150%); 2) Lung cancer: 18.2 (or 0.0182%); 3) Colorectal cancer: 15.4 (or 0.0154%)
Radon is a leading cause of cancer
According to the U.S. EPA, radon is the leading cause of lung cancer among non-smokers and the second leading cause among smokers claiming the lives of 20,000 people in the U.S. annually.
At the typical indoor radon concentrations of a home here in Maine (U.S. EPA) of over 4 pCi/L the U.S. EPA estimates a cancer rate of at least 700 per 100,000 (or 0.7%) for non-smokers and 6,200 per 100,000 for smokers (or 6.2%). At the U.S. national average household radon concentration of 1.3 pCi/L the estimated cancer rate is 200 per 100,000 (or 0.2%) for non-smokers and 2,000 per 100,000 (or 2%) for smokers.
Milk and ovarian cancer
According to the American Journal of Clinical Nutrition, which is published by The American Society for Nutrition, research conducted by the Division of Nutritional Epidemiology, The National Institute of Environmental Medicine, Karolinska Institutet, Stockholm (SCL and AW), and the Department of Surgery and the Center for Clinical Research, Uppsala University, Central Hospital, Västerås, Sweden (LB) found that women who consumed high intakes of four servings or more per day of dairy products (about 32 ounces of milk) had twice the risk of ovarian cancer than women who consumed less than two servings per day. According to the U.S. National Institute of Health's National Cancer Institute's Surveillance Epidemiology and End Results (SEER) report the ovarian cancer rate for women in 2003 was 13.2 per 100,000 (or 0.0132%). Thus, doubling one's risk would go from 0.0132% to 0.0264% (or a total increased risk of 13/1000 of a percent). Of course, this all assumes the 0.0132% was a baseline ovarian cancer risk.
Based on the numbers above, the ovarian cancer risk from drinking at least four glasses (32 ounces) of milk per day is over 7.5 times lower for non-smokers (75 times for smokers) than the cancer risk from radon at the normal indoor radon concentrations of 1.3 pCi/L. Furthermore, at the average Maine household radon levels of 4 pCi/L, even the consumption of four or more glasses of milk per day the cancer risk is 26.5 times less for non-smokers (284 times less for smokers) than that from radon.
The report by the AJCN and the numbers above does raise three questions for me. 1) How many of us drink 32 ounces of milk per day every day? 2) Wouldn't consuming that much milk seriously raise cholesterol levels and thus make heart disease a more significant risk than cancer? 3) How many of us have actually tested our homes for radon and then taken measures to mitigate any elevated levels of radon?
Another report by the American Journal of Epidemiology, which is published by The Johns Hopkins University School of Hygiene and Public Health reported that "milk-drinking is not a source of ovarian cancer risk independently of its fat content." Based on this report, the real risk isn't milk, but excess consumption of fat. In other words, just as we need to limit the quantity of fat we consume from other sources, we need to limit the amount of fat we consume from dairy products. Even if one did consume the extreme amounts of dairy products mentioned in the AJCN report above this could be mitigated by using low fat alternatives like skim milk. It would seem that the operative word to fat and ovarian cancer risk is "moderation".
Other reports I found published by the Ohio State University and the American Cancer Society found that milk actually reduced cancer risks for colon cancer. Like with so many foods, milk is not purely good nor purely bad and it is the quantity consumed that matters most.
Does a few thousandths of a percent really matter?
When looking at increases in the risk of cancer one must keep in mind that doubling or tripling one's risk of cancer may only increase one's risk by a few hundredths or a few thousandths of a percent. A report stating that something doubles your risk of cancer sounds very scary, but if that doubling of risk only changes one's total risk by a few thousandths of a percent, is it really that important or is it just a minor consideration?
Everything in moderation
It seems that everyday new reports come out that make apparently contradictory cancer claims about a specific food. The issue of cancer risk factors is much more complicated than a simple "this is good for you and that is bad for you" response. In the case of milk I have referenced one study that shows an increased risk of ovarian cancer and another that shows a reduced risk of colon cancer. One needs to not get caught by the hype in the news or on advocacy websites and instead take a measured approach to risk factors. Very often the health benefits and risks, especially where cancer is concerned, get terribly exaggerated by a misunderstanding of what the numbers really mean.
Always remember that cancer risk factors are only one part of the overall health risk equation. One must also weigh other health risk concerns. Maybe more than anything the most important factors in one's health are to eat a balanced and varied diet and to always eat in moderation. As the saying goes, "too much of a good thing is just too much."