Wednesday February 17 2016
Organic milk has high levels of omega-3 fatty acids
"Organic meat and milk could offer health benefits, study suggests," The Guardian reports.
The news is the conclusion of two reviews looking at the available evidence on the potential benefits of organic meat and milk compared to their conventionally-farmed counterparts. We decided to focus our efforts on the milk review, as it is the larger of the two studies.
The study found some differences in nutrient levels. While organic milk had more omega-3 fatty acids, linked to improved heart health, and was slightly higher in iron and vitamin E, it also had lower levels of iodine and selenium. Iodine is needed by the body to produce the thyroid hormone, and selenium helps to protect against cell damage.
Overall levels of saturated fat did not differ between the two production methods.
Importantly, we do not know if any of these results would actually have a significant impact on long-term health outcomes. Studies looking at this, such as a cohort or randomised study, would be required to provide some sort of answer.
In many cases, people prefer organic food and drinks for environmental and animal welfare reasons, so health issues may not be that important to them.
Where did the story come from?
The study was carried out by researchers from a large number of universities and research institutes across Europe, including Newcastle University, the Norwegian Institute for Biochemistry Research and Warsaw University of Life Sciences.
It was funded by the European Community and the Sheepdrove Trust. The latter is a charity that supports research into organic farming practices.
The study was published in the peer-reviewed British Journal of Nutrition on an open-access basis, so it is free to read online (PDF, 1.6Mb).
The UK media was split in its reaction. The Daily Telegraph reported that the study "sparked a row among nutritionists," some of whom claimed the results "stretch credibility". The Mail Online was uncritical of the study, saying it "found clear differences" between organic and conventional food, calling it a "landmark study". The Metro was also uncritical, suggesting that if you buy organic you could "give yourself a pat on the back".
The Guardian and The Independent took a more neutral viewpoint, providing quotes from the researchers, as well as critics of the research.
What kind of research was this?
This was a systematic review and meta-analysis of studies comparing the nutritional content of organically-produced and conventionally-produced fresh milk. The meta-analysis only looked at cows' milk, although the study as a whole reported on results from some trials on sheep, goat and buffalo milk.
Standard systematic review and meta-analysis techniques were used. However, all the included studies were considered to be at high or unclear risk of bias because they didn't report results or methods in full, or didn't give enough detail about possible confounding factors. This reduces the reliability of the results.
Ultimately systematic reviews and meta-analyses are only as good as the information you feed into them.
What did the research involve?
The researchers looked for studies published from 1992 (when legal standards for farms describing themselves as organic were introduced into the EU) and 2014. They pooled the data to get average figures, looking at specific nutrient levels in organic and non-organic fresh cows' milk.
They tested the results for reliability and came up with percentage differences for organic and non-organic milk.
The researchers also carried out a study to identify what might have caused the differences in nutrient levels. They used data from a big European farm survey to identify the practices linked to composition of organic and conventional milk.
They also investigated what other factors could have influenced their results, including geographical differences that could affect (for example) the nutrients in grass.
What were the basic results?
The main result that researchers found was a higher level of certain fatty acids – linked to better heart health – in organic milk. While levels of saturated fat and monounsaturated fat were about the same, organic milk contained slightly higher polyunsaturated fatty acid levels, including, on average:
- 56% more omega-3 fatty acid than conventionally-produced milk (95% confidence interval (CI) 38 to 74%)
- 69% more alpha-linoleic acid (95% CI 53 to 84%)
- 41% more conjugated linoleic acid (95% CI 14 to 68%); however, the effects of conjugated linoleic acid on human health are unclear from research
Looking at vitamins and minerals, the researchers found slightly higher levels of vitamin E and iron, but lower levels of iodine and selenium. Milk is not a major source of iron or vitamin E in the diet.
The researchers said that results varied a lot by country or geographic region. They said differences in cows' food explained much of the difference in nutritional levels, with more grazing on grass and silage (as is more common in organically-reared cattle) linked to higher levels of omega-3 fatty acids.
How did the researchers interpret the results?
The researchers said their results showed that switching from conventional to organic dairy farming, "will result in substantive improvements in milk fat composition," although they admit there are "virtually no studies in which the impacts of organic food consumption on animal or human health were assessed".
They said the results suggested that people wishing to increase their consumption of omega-3 fatty acids could switch to organic milk as a "complementary dietary approach". They say drinking the equivalent of half a litre of full-fat organic milk would provide an estimated 16% of the recommended daily allowance of omega-3 fatty acids, compared to 11% if you drank the same amount of conventional milk.
The arguments over whether organically-produced food is better for human health are unlikely to be resolved by this study. While the researchers have shown that some potentially beneficial fats are higher in organic milk than conventional milk, we don't know how much of an effect this would have on people's health.
Omega-3 fatty acids and alpha-linoleic acid have been associated with improvements in heart health, though causation has yet to be established. Indeed, the latest guidance from NICE does not recommend supplements of omega-3 for prevention of heart attacks, although it acknowledges that taking them does not appear to cause harm. In contrast, there's little evidence about the effect of conjugated linoleic acid on human health.
There are other factors worth bearing in mind. Firstly, the beneficial fats specified in this study are found in dairy fat, so would be a very small constituent of skimmed or semi-skimmed milk. Many people who want to protect their heart choose not to drink full-fat milk. Even if you did drink half a litre of full-fat organic milk a day, that would only give you a small proportion of the fatty acids recommended – and you would be getting the same level of saturated fats as drinking conventional milk. This would be 11g – over half the recommended 20g maximum daily saturated fat intake for women, or over a third of the 30g recommended for men.
The differences in vitamin and nutrient levels are small, and as the researchers note, the vitamins and minerals (vitamin E and iron) found at higher levels in organic milk are unlikely to have much effect on human health, as other foods provide much more of them in our regular diets.
Without good-quality studies that look at the effects on health of consuming mainly organic food, we can't really tell whether organically-produced food is better for our health.
It would be unwise to assume that organic foods and drinks are having a protective effect on your heart health if you neglect other important factors, such as your weight, exercise levels and alcohol consumption.
Read about the steps you can take to improve your heart health.