What do the research studies say?

Osteoporosis

The Nurses’ Health Study (NHS) cohort was formed in 1976.  Registered nurses from 11 states responded to a mailed questionnaire.  Follow-up questionnaires were mailed every 2 years until 1994.  The subjects provided information on their medical histories, lifestyle choices, diet, and risk factors for conditions such as cancer and heart disease.  This information has been used to investigate the links between diet, lifestyle and development of disease.  In terms of osteoporosis, a diet high in dairy products is believed to supply the calcium and vitamin D necessary to maintain strong bones.  One evaluation of the NHS found that having adequate vitamin D intake was associated with a lower incidence of osteoporotic hip fractures in postmenopausal women.  Diets high in calcium seemed to be less important.  High milk consumption, which is fortified with vitamin D, did not appear to decrease the risk of hip fracture.  There is no reason to believe, however, that consuming dairy products, was responsible for an increase in hip fractures.  It is likely that the increased incidence of osteoporosis in these women is due to a variety of interrelated factors.

Another study found that women who drank less milk during childhood and adolescence were more likely to suffer from fractures as adults.  In this study, 3251 white women were surveyed.  Their hip bone density was measured and they reported their milk intake during childhood and adolescence.  For women aged 20-49, bone mineral content was 5.6% lower for those with low milk intake (<1 serving/wk) versus those with high milk intake (>1 serving/d).  Low intake of milk during adolescence also correlated with a decrease in hip bone density.

One small study showed that a group of 50 children who avoided drinking milk for long periods of time and failed to supplement their diets with other calcium-rich food sources were more prone to fracture.  These children had lower bone mineral density and sustained more fractures than controls from their community that were matched for age and sex.

Diabetes

Type I diabetes is caused by a variety of genetic and environmental factors working together.  One study looked at the worldwide increasing incidence of type I diabetes and how nutritional habits correlated.  The incidence (per 100,000 per year) of type I diabetes in children was collected from 37 world areas, and the nutritional habits were assessed including milk, cereal and meat consumption.  From 1961 to 2000, this study found that the supply of milk and cereal to these areas of the world remained unchanged, but meat supply increased dramatically.  There was a strong and highly significant positive correlation with milk and type I diabetes throughout the study.  Over the course of the study, incidence of type I diabetes increased significantly with increasing meat in the diet.  This study showed that nutritional factors have an impact on the increasing incidence of type I diabetes worldwide, however further studies are needed to determine the interactions between genes and nutrients.

Cancer

A pooled analysis of 12 cohort studies conducted in 2006 investigated the link between dairy products and ovarian cancer.  A total of 553, 217 women were questioned about their dietary intake of dairy.  They were followed for several years and a total of 2,132 epithelial ovarian cancers were detected.  High intake of dietary vitamin D (> 400 IU/d) was associated with greater risk for ovarian cancer compared to <100 IU/d; however, risk was not present for overall intake of vitamin D.  A statistically significant risk of ovarian cancer was associated with high intake of lactose (>30g/d vs <10g/d); however there was not a higher risk observed with dietary calcium.  The study concluded that there was no statistically significant association between milk or calcium intake and ovarian cancer risk; however a weak association was noted between high lactose intake and ovarian cancer risk.

A study in 2005 compared cancer incidence data from 40 countries between 1993 and 1997 to food consumption data for those countries.  The study investigated the possible link between breast, ovarian and uterine cancers and diet.  For breast cancer, meat was most closely associated, followed by milk and cheese.  For ovarian cancer, milk was most closely associated, followed by animal fat and cheese.  For uterine cancer, milk was again most closely associated, followed by cheese and meat.  The authors hypothesized that animal-derived estrogens in milk and dairy products may be affecting the incidence of these cancers and advocated further studies.

Infectious Illness

A case study published in 2003 described an outbreak of Campylobacter jejuni that was strongly associated with consumption of raw milk.  Twenty people attended a meal at which raw milk was consumed; 15 people drank the milk and 13 of those became ill.  Six of the 13 who fell ill required medical attention.  C. jejuni was cultured from 5 of the 6 stool samples obtained.

In 2003, the MMWR reported a multi-state outbreak of Salmonella enterica serotype Typhimurium that was linked to a working dairy farm that sold raw milk products.  A total of 62 individuals developed symptoms over a period of approximately two weeks.  These included 40 visitors to the farm who consumed raw milk products, 6 household contacts, and 16 dairy workers.  Thirty-two food samples were taken from the dairy and 5 were positive for the Salmonella species responsible for the illness.  Four dairy workers were found to be asymptomatically infected.

In 2000, an outbreak of listeriosis among Mexican immigrants in North Carolina was linked to the consumption of Mexican-style fresh cheese.  Eleven pregnant women, one nonpregnant woman and one immunocompromised man were affected.  Five stillbirths, 3 premature births and 3 infected newborns resulted from the outbreak.  The cheese was made with raw milk from a single dairy farm.

The MMWR reported a 2005 outbreak of E. coli O157:H7 that was linked to consumption of raw milk.  Eighteen cases were identified over a 2 week period; median age was 9 years old.  Five patients were hospitalized and 4 of these developed hemolytic uremic syndrome.  E. coli O157:H7 was isolated from eight stool samples and raw milk samples from the dairy farm. 

In case reports of Salmonella Dublin infections in California from 1980-83, over one-third of the 303 cases were associated with raw milk consumption.  Outcomes were reported for 236 out of the 303 people affected; 69 people died from this outbreak.  Many of the patients had serious underlying health problems.

There was an outbreak of Salmonella Typhimurium linked to raw milk in New Mexico in 1983.  This bacterial strain was resistant to multiple antibiotics.  Of the 19 patients who provided food histories, 12 patients had ingested the same brand of raw milk in the 2 weeks prior to becoming ill. 

In Washington state, in December 2005, there was an E coli O157 outbreak that affected 16 people who drank raw milk from an unlicensed farm.

Exposure to the rabies virus occurred in Massachusetts in 1996 and 1998.  Rabid cows transmit the virus in their milk, and rabies can theoretically be present in unpasteurized milk.  Eighty people consumed the milk produced by the 2 rabid cows and 9 other people came in contact with the salvia from the infected cows.  All people involved received rabies prophylaxis and no human cases of rabies were reported.