Raw cow's milk has a higher content of Omega-3 fatty acids than does pasteurized, homogenized or low-fat milk, and epidemiologists are saying this explains why children who consume unpasteurized milk are less likely to develop asthma.

That has been the claim of raw milk drinkers, who point to less asthma in Amish communities. Epidemiology is often that technique; find a result, wonder about a cause, and see if two curves match. One of the curves is created using recall of things like diet.

Ludwig-Maximilians-Universitaet (LMU) in Munich researchers using the PASTURE birth cohort match the curves also, but go a step farther and say it isn't due to being raw, it is that the unpasteurized milk contains more omega-3 fatty acids. They don't recommend raw milk, since it is far more likely to contain pathogenic micro-organisms, but do seem to advocate Omega-3s to prevent asthma in their Journal of Allergy and Clinical Immunology paper.

PASTURE followed over 1,000 children living in rural areas, whose mothers kept diaries of their child's nutrition and it's illnesses up until the age of 6. The analysis found that the proportion of children who had developed asthma by that age was significantly lower in the cohort who had regularly consumed untreated farm milk.

"The effect can be partly explained by the higher overall fat content and the higher levels of omega-3 fatty acids found in farm milk," says Tabea Brick. According to the study, this effect is specific and can be clearly distinguished from the possible impact of other modulatory factors.

Omega-3 fatty acids have recently been deemed essential for human health. However, they cannot be synthesized in the human body and must therefore be obtained from dietary sources. The compounds are linked to various positive physiological effects.

Armed with dietary information,  the researchers assessed the composition of raw milk and shop milk that had undergone different degrees of industrial processing (pasteurization, homogenization, fat reduction). The results revealed that the level of omega-3 fatty acids remaining in the finished product was inversely proportional to the intensity of processing. In contrast, the content of omega-6 fatty acids, which mainly act as precursors for the production of pro-inflammatory modulators in the body, was virtually unchanged by any of the treatments used.

The standard industrial treatment process involves pasteurization of the raw milk at a temperature of between 72 and 75°C, and homogenization to avoid creaming of the milk. The authors of the new study argue for the development of milder methods of milk processing that will ensure the retention of beneficial components present in raw milk, while ensuring that potentially dangerous pathogens are effectively eliminated.