The raw milk debate — helping parents wade through the milk science
“Drink your milk and go outside and play.”
Generations have grown up drinking their milk. It’s long been recommended as a wholesome source of protein, vitamins, and calcium and other minerals, for growing bodies and for people of all ages. Nowadays, milk seems to have become complicated and controversial. Parents hear sensational claims of special health benefits and potentially harmful risks about both pasteurized and unpasteurized milk. Trying to decide which is the safest and healthiest choice for their children can be impossibly hard for parents, though, without knowing which claims are based on the best scientific evidence and which ones are fiction.
A paper in the new issue of Clinical Infectious Diseases revealed some surprising information about the safety and wholesomeness of milk that may help break through the milky maze.
Professors Jeffrey T. LeJeune, DVM, Ph.D., and Päivi J. Rajala-Schultz, DVM, Ph.D., at the Department of Veterinary Preventive Medicine at Ohio State University, reviewed the evidence on how milk can become contaminated, how it can be make safer, and trends in milkborne diseases among people in the United States.
Looks and intuition can be deceiving
Milk can become contaminated with organisms before cows or goats are milked, and during collection, processing, distribution and storage. The most striking finding in their report was that we can’t trust appearances to know if milk or a dairy animal is healthy or infected.
Healthy looking cows. One of the first surprises these animal experts discussed was an adage many of us probably believed: that milk from a healthy cow without mastitis (infection of the mammary gland), that’s had its teats sanitized prior to milking, means the milk is free from bacteria. Bacteria not only lives on the teat skin, they said, but also on the epithelial lining in the teat canal (the duct that carries the milk from the mammary gland to the teat opening). In healthy cows, Staphylococcus, Streptococcus, Bacillus, Micrococcus, Corynebacterium and even coliform bacteria colonize this area so that by the time the milk leaves the animal, it can already contain numerous bacterial contaminants.
The odds of a contaminated sample. Most of us know that mastitis is a significant way milk can become infected. Milk samples tested at laboratories with the University of Wisconsin in Madison and Cornell University in Ithaca, New York, found mastitis infections in up to half of the samples. Staphylococcus and Streptococcus species were the most common bacteria, found in about 20% of the milk, they said. But going to the original references cited in this paper revealed that infection rates appear to have dropped significantly between 1991 and 2001.
More specifically, while about 48.5% of the 108,312 samples tested by Cornell’s Quality Milk Promotion Services from dairy cows in New York and northern Pennsylvania in 1991-1995 were infected, rates were slightly lower (36%) among the cows enrolled in the Dairy Herd Improvement Association. Among more than 83,000 milk samples tested between 1994 and 2001 in Wisconsin, the percentage of contaminated samples dropped from 20.6 to 9.5% by 2001.
Healthy looking milk. Mastitis changes the appearance of milk, giving it an off color or specks of blood, and it isn’t sold for humans to drink. But it turns out that looks can be deceiving.
While only about one in ten of the Wisconsin milk samples from cows were infected, an important finding was that the infected milk from animals with subclinical mastitis infections looked no different from uninfected milk and had been added to the tank for sale. These animals appeared healthy, too.
Healthy looking farms. Herds can have their milk infected from their natural living environment. Nature is not sterile. The scientists at the Department of Dairy Science at the University of Wisconsin reported that animals are continually exposed to pathogens that can lead to mastitis because the primary route of contamination is contact with moisture, mud and manure on the farm. “Unlike mastitis caused by contagious pathogens, mastitis caused by environmental pathogens cannot be eradicated from a dairy herd,” they said. No matter how pristine a farm and well cared for it and the animals may be. Bacteria, we’re reminded, are all-natural.
Milk is contaminated from dairy farm environmental pathogens more commonly than most consumers might envision. According to the Ohio State professors, prevalence is:
<1% to 8.9% for Salmonella species
2.7% to 6.5% for L. monocytogenes
<1% to 3.8% for Shiga toxin–producing E. coli
<1% to 12.3% for C. jejuni
1.2% to 6.1% for Yersinia enterocolitica
Chilled milk. “[T]he rich nutrient composition and neutral pH make milk a good vehicle for the survival and growth of bacteria,” they wrote. With quick refrigeration and maintaining proper chilling, the bacterial proliferation can be suppressed (with the exception of Listeria species and other psychotropic organisms). But that’s not sufficient, given these natural levels of contamination, to prevent diseases in people, especially vulnerable populations.
Other disease pathogens can contaminate milk. The Ohio State University professors shared that veterinary preventive health measures have been successful in mostly eradicating two serious diseases in cows, Mycobacterium bovis and Brucella abortus, but others are still commonly found in the milk of asymptomatic cows and goats and contaminated milk.
These include Coxiella burnetii; Listeria species; Mycobacterium avium subspecies paratuberculosis [at least 68% of all dairy herds per USDA estimates in 2007] Campylobacter species; coliforms, including E. coli; and Salmonella enterica. Cattle can be a major reservoir of these organisms and still remain clinically healthy and maintain near-optimal milk production.
Keeping milk safe. Science has taken three tactics to minimize risks that milk is contaminated with organisms that can make people sick: animal health, improved milk handling hygiene and pasteurization. Most dairy producers take seriously the health of their animals and hygienic conditions on their farm for both the welfare of their animals and safety of their milk. Food safety practices on the farm to minimize exposures include maintaining sanitary milking facilities and cow cleanliness and milking processes.
Despite excellent veterinary care, however, there are a number of infections that may be present in animals even when they remain completely without symptoms. And completely controlling microbial contamination with milking hygiene is difficult, if not impossible in the dairy farm environment, they reported. This isn’t necessarily the fault of the dairy farm because pathogens can have multiple reservoirs, don’t always cause noticeable diseases in the animals, it isn’t completely known how some pathogens are spread, and cost-effective sufficiently sensitive diagnostic tests are not available for dairy farmers.
Professor LeJeune said he found a troubling percentage of 461 Ohio dairy farms he surveyed were unaware of the potential for many pathogens to make people sick. He reported that “36% did not think Salmonella species caused disease in humans. Likewise, 81%, 88%, and 91% of farmers indicated that Listeria, Cryptosporidium, and Campylobacter species, respectively, were not associated with disease in humans,” he wrote. Gads, these are significant sources for foodborne illnesses in people. It would be disturbing if dairy farmers had this poor an understanding, but the data isn’t published to examine more closely.
Clearly, coming from nature, milk isn’t sterile and, as we’ve seen, significant percentages of natural samples contain bacteria that can make people sick. That brings us to pasteurization, a simple process of heating milk for a period of time at a specific temperature to kill pathogens, invented more than a century ago by Louis Pasteur. Grade A pasteurized milk sold today follows the science and safety standards established by the U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition.
The temperature and time are determined by the number of bacteria found to be in the milk. Pasteurization doesn’t make milk sterile, but by killing the pathogenic (disease-making) and spoilage organisms, it is safer and won’t spoil as quickly. Milk has been pasteurized as part of public health service regulations in the United States since 1924 and has been adopted by every state in the country. Milk regulations are set within each state and the FDA’s only enforcement role was in prohibiting interstate shipment of unpasteurized milk for human consumption since 1987. More than half of states have also made the sale of raw milk illegal, although it’s still sold as animal or pet food or the law skirted by selling “shares” in cows.
Raw milk’s health benefits
The marketing claims surrounding unpasteurized milk often give consumers a confusing maze of conflicting health information. “Raw-milk advocates suggest that unpasteurized milk products are completely safe and that they can prevent and treat a wide spectrum of diseases, including heart disease, kidney disease, cancer and lactose intolerance,” the Ohio State University professors documented. Milk is also purported to contain substances that have bacteriostatic and antimicrobial properties and that pasteurization destroys them. “Scientific evidence to substantiate the assertions of the health benefits of unpasteurized milk is generally lacking,” the Ohio State experts said.
Pasteurization doesn’t cause appreciable losses in the levels or clinically meaningful (meaning: have an actual effect on the body or on human health, not just "measureable") activity of protein, vitamins, enzymes, milk sugars, immunoglobulin, and other components in milk, as they documented with clinical research.
“There is no credible or scientific evidence that raw milk produces any measurable health benefits,” Dr. Perry Kendall, M.D., British Columbia Provincial Health Officer, said in the Vancouver Province on December 19, 2008. “Pasteurization of raw milk simply heats the milk to kill disease-causing bacteria, exactly the same process as when one cooks poultry or meat. Pasteurization of raw milk has prevented thousands of illnesses and deaths and is one of the great advances of public health of the 20th century.”
According to Dr. Stephen Ostroff, M.D., a microbiologist and epidemiologist at the CDC before becoming the Director of the Bureau of Epidemiology of the Pennsylvania Department of Health, “some farmers are promoting raw milk in the mistaken belief that it is healthier or more nutritious.” But “the scientific evidence simply does not support this claim.”
Consumer choices and evaluations of the risks and benefits, however, don’t always follow the evidence or recommendations of experts. “This problem is particularly complicated by the fact that individuals with established attitudes not only seek information that is supportive of their views,” professors LeJeune and Rajala-Schultz said. There is also the natural human tendency to unconsciously process information in a way that supports what we want to believe and be vulnerable to various logical fallacies, they explained.
But is raw milk really as risky as scientists say?
According to the U.S. Centers for Disease Control and Prevention’s population surveys, about 3.5% of Americans had consumed unpasteurized milk sometime in the past week.
Weighing the risks of getting sick, consumer advisories from the FDA and CDC and virtually all scientific organizations, say that unpasteurized milk, no matter how carefully it’s produced, can be unsafe and that the risks are not worth it. Few parents would think to feed their children raw chicken, but might be tempted to believe raw milk is safer than the evidence suggests.
According to the FDA, raw milk does not kill deadly bacteria on its own and requires pasteurization to ensure these germs are removed. “Illnesses caused by pathogens found in raw milk can be especially severe for pregnant women, the elderly, infants, young children and people with weakened immune systems,” they warn. Pasteurization kills bacteria responsible for diseases such as listeriosis, salmonellosis, campylobacteriosis, typhoid fever, tuberculosis, diphtheria and brucellosis. Although most healthy young people will recover from these foodborne illnesses, some can be left with chronic and serious health problems.
Take campy, for instance, the single largest cause of foodborne illness in the world. Preventable Campylobacter infections kill more than 500 people each year in the U.S. and are indiscriminate in who they hurt, according to M. Ellin Doyle, Ph.D., with the Food Research Institute at the University of Washington in Madison. For example, this infection is responsible for up to 40 percent of the cases of Guillain-Barré Syndrome, the most common cause of acute paralysis in America, which afflicts up to 6,000 citizens each year. How many people have even heard about this risk?
While the repetition of advisories and publication of consumer information on risks of consuming raw milk has been said to be a conspiracy against raw milk vendors, the scientific evidence demonstrates this is not the case. Warnings to consumers about the risks of drinking raw milk have been stepped up over recent years because health professionals are trying to protect health and have seen a resurgence in milkborne diseases that had dropped dramatically with pasteurization, as raw milk has become trendy and its marketing has increased.
According to professors LeJeune and Rajala-Schultz, between 1880 and 1907, prior to pasteurization and improved food safety practices, there were about 29 outbreaks of milk-borne diseases every year in the U.S. This contrasts to an average of just 2.4 per year between 1973 and 1992 as pasteurization was widely adopted, according to the CDC.
But in the most recent 19 years (1993-2006), the number of outbreaks associated with unpasteurized milk has doubled to more than five a year. “Although some of this increase may be a result of increased detection and reporting, it is clear that disease associated with the consumption of raw milk is still an important public health concern in the United States,” the professors emphasized. They went on to describe numerous examples from CDC published reports of illnesses from Department of Health data.
According to the CDC's Morbidity and Mortality Weekly Report on March 2, 2007, for example: “From 1998 to May 2005, CDC identified 45 outbreaks of foodborne illness that implicated unpasteurized milk, or cheese made from unpasteurized milk.” Outbreaks are not the same thing as individual cases. “These outbreaks accounted for 1,007 illnesses, 104 hospitalizations, and two deaths,” the CDC added. “The actual number of illnesses was almost certainly higher because not all cases of illness are recognized and reported.”
The FDA CFSAN said that more than ten outbreaks from raw milk or raw milk cheese were reported to the FDA in 2005-2006. According to the Director of the Dairy and Egg Safety Division at the FDA CFSAN, in testimony on raw milk safety presented to the Ohio House of Representatives Agricultural Committee on May 24, 2006, a search of their data from 2000-2005 “produced 44 illnesses associated with pasteurized milk products as compared with 473 from raw milk… many of them children and pregnant women.” There were seven deaths, including three infant fatalities.
In other words, raw milk has been linked to more than 90% of the cases of milk-borne illnesses, ten times the number linked to pasteurized milk.
Yet, only about 3.5% of American consumers drink raw milk. To put the potential risks into further perspective, the amount of raw milk consumed appears considerably less than pasteurized, even in states where it is legal: “Consumption of raw milk has been found to account for less than 1% of total milk sold in the states that permit the sale of raw milk.” [The media, on the other hand, gives us the impression that everybody who's anybody drinks raw milk!]
One of the frightening exposures occurred in Oklahoma in 2005 when a dairy cow was confirmed to have rabies and milk from the infected cow was sold to an estimated 10,000 consumers. State health departments conducted emergency post rabies assessments and people at highest risks (immuno-compromised and with open mouth sores) received rabies shots at an estimated cost of $186,000. “Pasteurization of milk would have made any rabies virus present in milk ineffective,” said the FDA.
An outbreak of E.coli 0157:H7 infections linked to raw milk from a cow share program among five cows in Washington and Oregon in December of 2005 resulted in 18 cases of illness (half were young children), five people were hospitalized, and two children developed Hemolytic Uremic Syndrome. “DNA ‘fingerprints’ (PFGE) of E. coli O157:H7 recovered from samples of raw milk obtained from cow-share customers, from farm environment, and from swabs of cattle all matched,” according to the CDC.
This review in Clinical Infectious Diseases concluded by stressing that the key way to prevent milk-borne illnesses is to avoid consuming raw milk. Raw milk is especially risky for children, women of child-bearing age, elderly and those with compromised immune systems.
When 90% of these illnesses, and so much suffering and so many needless deaths, might have been prevented with something so simple that science has had available for around a century, it’s understandable healthcare professionals are trying to get the message out. Sound science isn’t a conspiracy. Milk is a wholesome food packed with nutrients, but please make it pasteurized.
© 2009 Sandy Szwarc
Addendum: This post, like all posts, was written after carefully reviewing all sides, including recent rebuttals by raw milk advocates, marketing claims, the original research and medical data. Raw milk claims proved frighteningly unsound, unscientific, and offering potentially dangerous medical advice for young parents, children and elderly. It is hoped that this information on the CDC and FDA data, as well as the CID report and the reviews of medical experts, will help you protect yourself and your family.