Earlier this year, Newcastle University issued a press release which claimed that cows grazing on organic farms produced milk that was "significantly higher in beneficial fatty acids, antioxidants and vitamins".

How beneficial? Very beneficial, as all of these chemicals "have been linked to a reduced risk of cardiovascular disease and cancer". How much higher? According to the press release, one of the beneficial fatty acids, conjugated linoleic acid (CLA), was 60% higher in the organic milk than in conventional milk. The Daily Mail was beside itself, quoting the figure in an article: "Drinking organic milk 'may cut risk of heart disease and cancer'".
The Newcastle study was published in the Journal of the Science of Food and Agriculture. Cows that ate grass and clover instead of grain exhibited higher levels of CLA, alpha-linoleic acid (ALA), alpha-tocopherol (vitamin E) and three carotenoids (beta-carotene, lutein and zeaxanthin) in their milk than conventionally-reared cows.

Grass-fed cows raised conventionally had still higher levels of these compounds in their milk, but the media did not mention this fact. Milk obtained in the winter months from all three groups had the same nutrients because the cows ate indoors. There are no clinical trials demonstrating that beta-carotene or vitamin E prevent cancer or heart disease, although it is assumed that they are part of a defence system that includes many other antioxidant chemicals in food. Epidemiological studies have been conflicting. Clinical trials involving high doses of beta-carotene/vitamin A and beta-carotene/vitamin E had to be stopped because the supplements were increasing instead of decreasing cancer deaths.

Some promise

ALA is a member of a class of fatty acids known as omega-3 fatty acids, two of which have shown some promise in animal and epidemiological studies as preventives in cancer and coronary heart disease. These two acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found in fatty fish, unlike ALA. EPA and DHA have different chemical structures from ALA and the bulk of the research that has been done on them shows promise. At least one study concluded that EPA and DHA may reduce the risk of total and advanced prostate cancer in humans but "increased intakes of ALA may increase the risk of advanced prostate cancer".

CLA has also received a good press, but mainly because of results in mice where it appears to be effective in reducing body fat and plasma lipids. A review of human studies, however, reported that "none of the studies found a significant reduction in body weight, and only two studies showed a significant but relatively small body fat-lowering effect".

Furthermore, it found no significant effects of CLA on triglycerides, low density lipoprotein, high density lipoprotein and total cholesterol plasma concentrations in humans. None of this was addressed by the Newcastle group. CLA has proved effective in lowering breast and colon cancer in rodents, but there is scant evidence for this effect in humans.

The Newcastle group claimed organic milk contained 39% more ALA and 33% more carotenoids than conventional milk. Vitamin E also went up by 33% and vaccenic acid, a fatty acid that is converted to CLA by humans, jumped 58%.

Large percentage increases, however, mean absolutely nothing if we are dealing with very small quantities to begin with. For example, a litre of conventional milk contained 860 micrograms of vitamin E compared to 1,140 micrograms in what I will call "Newcastle University organic milk". The US government's recommended daily allowance for vitamin E for adults is 15,000 micrograms a day, which means that you would have to drink over 12 litres of Newcastle University organic milk every day in order to satisfy US nutrition guidelines. Milk, whether conventional or organic, is not high in vitamin E.

Nor is Newcastle University organic milk a good choice for beta-carotene, as one would need to drink 50-170 litres a day to obtain the recommended daily allowance of 15-50 milligrams beta-carotene a day.
And if age-related macular degeneration is what you're worried about, you will have to drink about 150 litres every day to get all the lutein and zeaxanthin you need (6 milligrams each day) according to the American Optometric Association .