Epidemiology

How do scientists know that smoking causes cancer? How do they know that alcohol and tobacco cause birth defects? How can we be sure that high cholesterol causes heart disease? The answers to these—and many of our other most important health questions—come from epidemiology: the study of illness patterns in groups and the application of the findings in order to control health problems. Epidemiologists collect data on who gets sick and then use rigorous statistical analysis to scientifically determine which common lifestyle choices, environmental factors, and genes are behind various illnesses.

Unlike nonhuman-animal data, which can never be directly applied to the human condition, epidemiology produces powerful human data that immediately give doctors and patients new ways to prevent and treat disease. Unfortunately, these human studies are often underutilized because they require more time and effort than animal studies and because researchers can more easily advance their careers by publishing lots of meaningless papers on animal experiments. That's why the public needs to speak up and demand that its tax dollars only go toward lifesaving human research, such as the three main types of epidemiology: population comparisons, longitudinal studies, and clinical trials.

Population Comparisons

Population comparisons involve contrasting the health data of different demographics, such as different races, sexes, occupations, or nationalities. For instance, numerous studies have documented that Asian women have far lower rates of breast cancer than do American women. This fact led scientists to conclude that either Asians are genetically protected from breast cancer or the American lifestyle causes breast cancer. Further epidemiological studies showed that Asian-American immigrants have the same rate of breast cancer as do other Americans, confirming that lifestyle factors—and not genetics—are behind America's high rates of breast cancer.

T. Colin Campbell, author of the largest and most respected epidemiology study ever, The China Study, concluded that the large amounts of fat and animal protein in American diets were the key traits differentiating American and Asian populations. Campbell's international analysis shows that both animal fat and animal protein, but not plant fat, are closely associated with breast cancer.¹ His hypothesis has been confirmed by The China Study 2, which showed that as the Chinese have adopted a Western diet, their breast cancer rates have risen.

Longitudinal Studies

Longitudinal studies follow a large group of participants—called a "cohort"—for a long period of time, recording extensive data about their lifestyles and seeing who gets sick. These studies produce massive amounts of data on a wide range of lifestyle factors and illnesses.

Perhaps the best-known example of such a study is The Nurses' Health Study, which was organized by Harvard University and tracks the health of more than 100,000 nurses across the country. For decades, these nurses have filled out questionnaires, undergone physicals, and submitted blood, urine, hair, and toenail samples for analysis. Among the many groundbreaking findings of the study was the discovery that—contrary to dairy industry claims—the women who consumed high levels of dairy products had the highest rates of osteoporosis.²

Clinical Trials

Clinical trials are controlled longitudinal studies in which the researcher manipulates a single variable between groups. In drug testing, for example, one group might be given a full dose of the drug, the second group a half dose, and the third group a placebo (sugar pill). The patients are randomly assigned to the different groups and don't know which one they're in (in a "double-blind" study, even the researchers don't know who is in which group until the trial ends). Because these studies are controlled, different outcomes between the groups can be attributed directly to the treatment.

One of the most famous clinical trials in history is the Women's Health Initiative (WHI), in which over 160,000 postmenopausal women are participating in trials on hormone replacement, dietary modification, and the use of calcium and vitamin C supplements. So far, the astounding revelations of WHI include the discovery that taking Premarin (horse-urine-derived estrogen plus Progestin) for hormone replacement increases women's risk of heart disease, stroke, and breast cancer. These results discredited animal studies that had suggested that Premarin would protect against heart attack and stroke. Because scientists relied on misleading animal studies instead of promptly conducting extensive clinical trials, millions of women unknowingly put themselves at risk.³

Take a look at other recent epidemiological findings for the following major illnesses:

• Alzheimer's Disease
• AIDS
• Heart Disease
• Diabetes
• Cancer

Alzheimer's Disease

• Researchers at the University of Utah have discovered that overweight women have an increased risk of developing Alzheimer's disease. The study tracked 392 women who were 70 years old at the beginning of the study for 18 years and looked at which participants developed Alzheimer's. The researchers found that the women who developed Alzheimer's had an average body mass index (BMI) of 29, while those women who remained healthy were slimmer, with an average BMI of just 25.⁴
• A study published in the journal Neurology found that heart disease and Alzheimer's have many of the same risk factors, including high cholesterol and diabetes. Researchers followed 9,000 people for 27 years and measured signs of dementia, the key symptom of Alzheimer's. They found that high cholesterol increased the risk of developing dementia by 42 percent and that those with diabetes at ages 40 to 45 had a 46 percent increase in the risk of developing dementia. Both high cholesterol and diabetes are largely tied to dietary choices-mainly meat—based diets high in saturated fat and cholesterol.⁵
• Since high cholesterol is tied to increased rates of dementia and Alzheimer's, researchers have investigated whether cholesterol-lowering statins can prevent dementia. However, a 2005 study published in the Archives of General Psychiatry reports that statins do not lower the risk of developing dementia or Alzheimer's. These results suggest that reducing the risks associated with high cholesterol can only be accomplished through a diet low in cholesterol and saturated fat.⁶

AIDS

• The discovery of AIDS/HIV was accomplished through a classic use of epidemiology. In the early 1980s, HIV remained undiscovered and doctors knew only that unusual numbers of patients were succumbing to rare infectious illnesses, suggesting a mysterious immune-system disease. By epidemiologically tracking who contracted the disease, researchers quickly discovered that AIDS was caused by a virus transmitted through unprotected sex, blood transfusions, or intravenous drug use with a shared needle.
• In February 2005, the death of a New York City AIDS patient revealed a deadly new strain of HIV—one resistant to all current treatments. Using epidemiology and advanced blood-testing techniques, scientists acted quickly to prevent a new epidemic of untreatable AIDS. Epidemiologists first traced the sexual histories of the deceased victim and all his partners. Blood tests then revealed to whom the virus had been transferred, allowing doctors to isolate and contain the disease before it spread.⁷

Heart Disease

• Because of the cost and side effects associated with cholesterol-lowering statin drugs, physicians recommend lowering cholesterol through lifestyle changes such as diet and exercise. The best cholesterol-reducing diet is a low-fat vegan diet, and a study by physicians at the University of Toronto has now proved that a vegan diet lowers LDL (bad) cholesterol at least as well as statins do. The study also found that a vegan diet lowers cholesterol three times more than does a low-fat diet that includes meat and dairy products.⁸
• Heavy exposure to secondhand smoke causes heart attacks. In 2002, Helena, Montana, banned smoking in indoor public spaces. Hospital records show that after the ban was enacted, heart attack rates fell by 40 percent. However, Helena's clean-air law was struck down in court six months later, and indoor smoking was resumed. Once citizens were again exposed to smoke-filled bars and restaurants, heart attack rates quickly returned to pre-ban levels. Centers for Disease Control and Prevention epidemiologists now blame secondhand smoke for 35,000 cardiac-related deaths a year, and the Helena data suggest that the numbers might be even higher.⁹

Diabetes

• The Diabetes Prevention Program was a major government study that proved that lifestyle changes can prevent or delay the onset of type 2 diabetes. For three years, the study followed 3,234 overweight individuals who had high risk factors for diabetes. One group was given intense instruction on following a low-fat diet and exercising, another group received a drug, and the last group only got a placebo. The study found that the diet-and-exercise group had phenomenal success in preventing diabetes as compared to the other groups—it had an almost 60 percent reduction in diabetes rates. Based on these results, the government is shifting the way that it approaches the diabetes epidemic to focus less on "cures" and more on prevention.
• Another government study, The Diabetes Control and Complications Trial, showed that strict blood-glucose control can prevent or delay the complications of type 1 and type 2 diabetes, including heart attacks, strokes, blindness, kidney failure, nerve damage, and amputations. The 1,441 diabetic participants maintained either a standard-care regime or a stricter monitoring of blood sugar and insulin levels. The strict-treatment group boasted a 50 to 75 percent reduction in all major complications as compared to the standard-treatment group. The study proved that with early treatment, diabetes can effectively be managed, reducing patient suffering and health care costs.

Cancer

• A decade-long American Cancer Society study of 148,610 people has conclusively shown that meat consumption is linked to colon cancer. Particularly bad are red and processed meats, which raise colon cancer rates by 50 percent when eaten regularly.¹⁰
• Researchers at the Dana-Farber Cancer Institute have found that aspirin is effective at fighting colon cancer. Their study of 846 patients with colon cancer found that those taking aspirin had a 55 percent reduction in their chance of cancer recurrence. Moreover, their chance of dying two and a half years later was 48 percent lower. This study presents a valuable alternative to more risky and expensive drug treatments.¹¹
• Researchers at the Johns Hopkins School of Medicine have shown that secondhand smoke can lead to cervical cancer. It has long been known that women who smoke are more likely to contract the disease, but this new study shows that women who live with a smoker are also twice as likely to develop cervical cancer. This finding is important evidence in the ongoing controversy over the dangers of secondhand smoke.¹²

---

1. T.C. Campbell, The China Study: The Most Comprehensive Study of Nutrition Ever Conducted (Benbella Books, 2005) 83-89.
2. D. Feskanich, W.C. Willet, M.J. Stampfer, and G.A. Colditz, "Milk, Dietary Calcium, and Bone Fractures in Women: A 12-Year Prospective Study," American Journal of Public Health 87 (1997): 992-7.
3. Writing Group for the Women's Health Initiative Investigators, "Risks and Benefits of Estrogen Plus Progestin in Healthy Postmenopausal Women," Journal of the American Medical Association 288 (2002): 321-333.
4. Rob Stein, "Study Links Excess Weight to Risk of Alzheimer's," The Washington Post 15 Jul. 2003.
5. Maggie Fox, "Risk Factors for Heart Disease, Alzheimer's Similar," Reuters, 24 Jan. 2005.
6. "Statins Don't Protect Against Dementia: Study," Reuters, 10 Feb. 2005.
7. Lawrence Altman, "The Challenge of Tracing a Rare HIV Strain," New York Times 1 Mar. 2005.
8. "Diet Lowers Cholesterol as Well as Drug—Study," Reuters, 7 Feb. 2005.
9. Mark Kaufman, "Secondhand Smoke Poses Heart Attack Risk," The Washington Post 23 Apr. 2004.
10. "High Red Meat Consumption Linked to Colon Cancer," Reuters, 11 Jan. 2005.
11. Eric Nagourney, "Prevention: Aspirin May Fight Colon Cancer," New York Times 24 May 2005.