FAQ- Meta-Analysis on Nutritional Quality of Milk

Frequently Asked Questions About the Study:

“Higher PUFA and omega-3 PUFA, CLA, α-tocopherol and iron but lower selenium concentrations in organic milk: a systematic literature review and meta- and redundancy analyses.” February 16, 2016.  British Journal of Nutrition

Authors: Dominika Średnicka-Tober, Marcin Barański, Chris J. Seal , Roy Sanderson, Charles Benbrook, Håvard Steinshamn, Joanna Gromadzka-Ostrowska, Ewa Rembiałkowska, Krystyna Skwarło-Sońta, Mick Eyre, Giulio Cozzi  Mette Krogh Larsen, Teresa Jordon, Urs Niggli, Tomasz Sakowski, Philip C. Calder, Graham C. Burdge, Smaragda Sotiraki, Alexandros Stefanakis, Sokratis Stergiadis, Halil Yolcu, Eleni Chatzidimitriou, Gillian Butler, Gavin Stewart and Carlo Leifert

See also:

Major Findings

Q: What is a meta-analysis?

A: Meta-analysis is a statistical tool to extract more robust insights from several different studies focused on the same basic question, like “does organic milk offer nutritional advantages for consumers, compared to milk from cows on conventionally managed farms?”  Or, do drugs of “X” class prevent cardiovascular disease?

Scientists have continuously improved the sensitivity and rigor of meta-analyses methods. The University of Newcastle study team includes leading experts in meta-analysis methods. Its findings are based on the most sophisticated and recommended methods for the conduct of a meta-analysis on the impacts of farming systems and technology on the nutrient content of food.

Q: What were this study’s key findings?

A: Organic milk and dairy products are healthier because they contain higher levels of health-promoting omega-3 fatty acids, including more very long-chain omega-3s. Organic milk and dairy products also have a far healthier mix of fatty acids.

The concentration of health-promoting, total poly-unsaturated fatty acids (PUFAs) in organic milk and dairy products was, on average, 7% higher than in corresponding milk and dairy products from conventionally managed livestock farms.

The levels of health-promoting omega-3 fatty acids in dairy products were, on average, 46% higher than in conventional milk and dairy products. Importantly, the overall concentration of the critical, very long-chain omega-3 fatty acids was 58% higher in organic versus conventional diary products. In addition, the concentration of the heart-healthy fatty acid CLA (conjugated linoleic acid) was 34% higher in organic milk and dairy products.

The ratio of omega-6 to omega-3 fatty acids was also 79% lower in organic milk and dairy products, an important advantage for individuals dealing with or working to avoid heart disease, diabetes, chronic inflammation, and overweight. The typical balance in omega-6 to omega-3 fatty acid intakes in the U.S. is 10:1 to 15:1, a range that is clearly a risk factor for a number of chronic health problems.

Most governments recommend dietary patterns that keep this key ratio below 4:1, and epidemiological studies point to a ratio of about 2:1 for individuals who want to minimize cardiovascular disease (CVD) risk (i.e., there are no known additional health benefits from lowering the overall ratio in a person’s diet below 2:1).

[Note to readers – see Good Fat, Bad Fat and this detailed primer on different types of fat].

There are nutritional advantages linked to organic milk consumption beyond fat levels and quality. The Newcastle meta-analysis found that organic milk contains, on average, significantly higher levels of α-tocopherol (Vitamin E) and iron (Fe), but lower concentrations of iodine (I) and selenium (Se), compared to conventional milk.

Meta-analyses also identified trends towards higher vitamin A, ß-carotene, lutein and zeaxanthin, potassium (K), and lower copper (Cu) levels in organic milk, but further studies are required to confirm these results.

Milk is not a major dietary source for iron, Vitamin E and selenium, and the differences found were small and so unlikely to have a major nutritional impact. However, milk and dairy products are important sources of iodine. For detailed information on iodine see Scientific Advisory Committee on Nutrition (2014), Chambers (2015) and WHO (2015), and the two iodine-related FAQs below.

Q: How important is the finding that iodine levels are lower in organic milk?

A: The Newcastle team reported that, on average, iodine levels in organic dairy products are lower than in conventional dairy products: 147 ug/l in organic milk, compared to 248 ug/l in conventional milk.

Because of widespread use of kelp-based feed supplements and the feeding of other iodine-rich feeds by many U.S. organic dairy farmers, iodine levels in most of the organic dairy products on the market today are higher than the average reported in the University of Newcastle study. Typical levels in organic milk are, furthermore, adequate to meet the higher needs of pregnant women.

Q: How much iodine intake do government health agencies recommend?

A: Government health authorities have established a number of benchmarks governing daily iodine intakes among adults, as well as somewhat higher target intake levels for pregnant women. Some benchmarks recommend average, adequate daily intakes, others are based on the minimum daily intake needed to prevent disease, while a third set address maximum, safe long-term intake levels.

The upper safe limit in the U.S., New Zealand, and Australia for iodine intake for adults is 1,100 μg/day, while the UK upper safe limit is 1,000 ug/day.

Ingestion of less than about 100 ug/day of iodine increases the chance of health problems, and in particular goiter.

Different countries and medical associations have set different, recommended daily iodine intake levels, and indeed this target intake level has recently been raised, or is under review in many countries. Most recommended, safe daily iodine intake levels fall within the range established by the safe upper limit (~1,100 ug/day) and the necessary lower intake level (~100 ug/day).

Implications for Consumers

Q: Are these differences important to consumers, given typical levels and patterns of milk and dairy product consumption in the U.S.?

A: Government health authorities recommend that consumers double their very long-chain (VLC) omega-3 intakes to at least around 250 mg per day. The European Food Standards Agency (EFSA) also recommends that average VLC omega-3 intakes (especially of DHA) should be increased by 100-200 mg per day in pregnant and breastfeeding women.

A switch to consuming organic milk and dairy products will help consumers increase VLC omega-3 intakes, and without adding to milk fat consumption or overall or calories. The Newcastle University group estimate that consuming ½ litre of conventional full-fat milk (or equivalent dairy products) would supply 11% of the recommended daily intake of VLC omega-3 fatty acids, a share that would rise almost 50% (from 11% to 16%) with organic dairy products.

The major finding in another, unusual human study should be noted. It came from a human cohort in the Netherlands, and focused on the effect of organic milk consumption on eczema in infants from birth through age two. It found that eczema was significantly reduced in children from families consuming organic milk, rather than non-organic milk (Kummerling et al. 2008). The authors hypothesize that this impact may have been caused by the higher omega-3 fatty acid concentrations in organic milk, since there is increasing evidence for anti-allergic effects of omega-3 fatty acids (Calder et al. 2010).

How does this study improve upon earlier ones?

Q: How does this University of Newcastle study differ from earlier meta-analyses on milk and dairy products?

A: The conclusions of the new study from the University of Newcastle differ significantly from two other meta-analysis studies published in 2009 and 2012 (Dangour et al., 2009; Smith-Spangler et al., 2012).

Both earlier studies reported no significant differences in the nutritional composition of organic versus non-organic meat and dairy products. There are two major reasons why the results of the University of Newcastle study differ so dramatically.

First, the University of Newcastle team based its dairy product meta-analysis on 170 studies that met a series of strict, quality-based inclusion criteria. The earlier Dangour et al (2009) study was based on only 12 studies focused on dairy products (all of which were also included in he Newcastle study), while the Smith-Spangler et al (2012) team identified 37 studies.  Fortunately, several high-quality studies on the impacts of dairy farm management systems on milk nutritional quality have been conducted and published since 2012.

As a result, the University of Newcastle team had a much larger and higher-quality science base to draw upon in conducting its meta-analysis. If either the Dangour or Smith-Spangler led team had access to the larger and more robust list of studies accessible to the Newcastle team, it is likely their results would have been similar to those reported by the Newcastle team, despite modest differences in inclusion criteria and meta-analysis methods.

Second, because of the smaller number of studies available to the Dangour and Smith-Spangler-led teams, they chose to combine results for meat and dairy into one product group. This methodological step made it possible for them to include an ample number of comparisons for meta-analysis, but also had the effect of muddying the results, because of differences in how the nutritional composition of milk, in contrast to meat, varies as a result of organic versus conventional management.

Interestingly, Dangour et al. reported a trend towards significantly higher levels of poly-unsaturated and omega-3 fatty acids in organic livestock products (meat and milk) in their full report to the U.K. Food Standard Agency (the study sponsor) (Dangour et al. 2009b), but this was not mentioned in the published paper or press release.

Impacts of Milk Production

Q: What important new insights have been gained on the impacts of organic milk production?

A:

  1. Livestock production methods affect milk nutritional quality.

Organic production standards require that dairy cows have access to the outdoors and pasture. Organic farmers worldwide feed lactating cows much less corn and grain concentrates than conventional farmers, and rely more heavily on grazing and other forage-based feeds.

  1. Organic milk and dairy products contain higher concentrations of health-promoting fats, and generally lower levels of fats that promote heart disease and inflammation.

The differences are most significant within the poly-unsaturated group of fatty acids. Organic dairy products contain much more desirable levels of total and specific omega-3 fatty acids, long-chain PUFAs, and conjugated linoleic acid (CLA).

  1. Consumption of organic milk and dairy products can improve overall diet quality, and reduce the risk of several diet-driven, chronic health problems.

Milk and dairy products are a substantial source of calories, protein, and omega-3 fatty acids in the U.S. diet. There is strong evidence that the differences in the fatty acid profile of organic versus conventional meat improve long-term health trajectories across the U.S. population by reducing the risk of heart disease, diabetes, certain cancers, dementia, and obesity.

One study in the U.S. projected the impact on a person’s omega-6 to omega-3 intake ratio as a result of switching to full-fat organic dairy products, coupled with avoiding at least one serving of food daily that is high in total omega-6 fatty acids (e.g., potato chips, any food fried in corn or soybean oil) (Benbrook et al 2013). The results were encouraging. These two changes in food choices would lower a person’s overall diet omega-6 to omega-3 ratio from around 11:1 to about 5:1, over half of the reduction needed to reach the heart-health sweet spot, 2:1.

Q: Why are organic dairy products healthier?

A: What lactating dairy cows eat determines how nutritious their milk is for us. Cows on organic farms consume, on average, much more grass and legume-based forage feeds, and much less corn, soybean, and other grain-based concentrates.

Grasses and forage legumes like clover hay are the building blocks of heart-healthy omega-3 fatty acids, while corn, soybeans, and other grains contain nutrients that animals transform into a far less-healthy mix of fatty acids.

Organic livestock production standards are strictly regulated in the U.S. and the European Union. Any food bearing the USDA “certified organic” label must legally meet standards set forth by the National Organic program (NOP). Organic standards require that livestock must have access to the outdoors and pasture during the growing season and/or when weather conditions permit.

In addition, on-farm economics plays a key role. Certified organic feed grains are expensive in the U.S. and Europe, and there are periodic problems with both supply and feed quality. For this reason, organic dairy farmers strive to incorporate as much home-grown forage as possible in the diets of their cows.

The cheapest pounds of milk produced on either conventional or organic dairy farms typically occur during the days when lactating cows are getting all, or most of their daily feed rations from actively growing grasses and legumes. This is especially true on organic or grass-fed dairy operations that have mastered intensive, rotational grazing systems.

Q: Does the breed of dairy cow and milking frequency impact milk nutritional quality?

A: Studies included in the meta-analyses suggest that traditional breeds can have a positive effect on milk quality, especially concentrations of omega-3 fatty acids (e.g., see findings in Stergiades et al. 2015).

High milking frequency and/or robotic milking also appears to have negative effects on milk quality, including somatic cell count (and indicator of a latent infection in teats) (Stergiades et al. 2012). But the effect of milking frequency and cow genetics is typically smaller than the impact of high-forage rations.

It is important to note that research also shows that the ability of traditional breeds (e.g., traditional Braunvieh) to generate milk with higher omega-3 levels compared to modern breeds (e.g., holstein and Brown-Swiss) depends on cow access to ample amounts of high-quality forages (75%-100% dry matter intake). When grazing and forages make up 25-49% of daily dry matter, the difference in omega-3 fatty acids between traditional and modern breeds is generally not significant.

Q: Why do organic standards alter milk quality?

A: Hundreds of controlled experimental studies in the U.S. and Europe conclude that differences in the fatty acid profiles of organic and conventional milk are primarily driven by differences in what lactating cows eat.

Studies comparing milk quality from forage-based diets, compared to the grain-based diets typical for intensive, conventional livestock systems, consistently show that forages result in higher levels of PUFA, omega-3 fatty acids, and CLA. The shifts in fatty acids in milk is directionally similar to the fatty acid changes in meat produced by organic, forage-based farms, in contrast to conventional or organic farms that feed significant amounts of grain and concentrates.

Q: Can non-organic, “grass-fed” systems deliver high milk quality?

A: Pasture-based and “grass-fed” dairy systems that are not certified to organic farming standards have been shown to produce milk with fatty acid, antioxidant and mineral concentrations that are very similar to organic systems, as long as the comparison farms are equally dependent on grazing and forage-based feeds.

However, in one key study, there were small, but significant milk composition differences (e.g. higher omega-3 and lower CLA concentrations) reported in milk from organic, grass-based farms, in contrast to similarly grass-based conventional farms. Redundancy analysis suggests that the differences arise from higher clover and lower grass content in most organic pastures (Stergiades et al. 2015).

About the Study

Q: Who conducted and funded the study?

A: An international team of 25 scientists carried out the study over a three-year period. The team was led by Dr. Carlo Leifert, University of Newcastle, Northumberland, UK. The team included one U.S. scientist, Charles Benbrook. Benbrook’s contributions to the study were carried out while he was a Research Professor at Washington State University (position ended May 15, 2015).

The total cost of the meat and dairy meta-analyses conducted by the Newcastle team was about $600,000 Euro, of which about 75% came from research grants from the European Commission, and ~25% was from the Sheepdrove Trust, a U.K.-based philanthropic institution.

The entire database generated and used for this analysis is freely available on the Newcastle University website (http://research.ncl.ac.uk/nefg/QOF) for the benefit of other experts and interested members of the public.

Q: Why was the study carried out?

A: Consumer interest in the safety, nutritional quality, and environmental impacts of organic food and farming has grown steadily over the last two decades. While nearly 400 studies have assessed the impacts of organic farming on the nutritional quality of organic fruits, vegetables, grains, and nuts, fewer research projects have focused on organic milk and dairy products. In addition, until this study, there has been no meta-analysis published in the open scientific literature focused on the nutritional quality attributes of organic milk and dairy products.

The European Commission recognized this gap in published studies, and provided the support needed by the University of Newcastle team to carry out this study on organic milk and dairy products. The European Commission also supported a 2014 study led by Dr. Leifert that was focused on the nutritional differences in organic versus conventional plant-based foods, published in the British Journal of Nutrition in July 2014 (Baranski et al. 2014). A meta-analysis on organic meat was also published February 16, 2016 in the British Journal of Nutrition (Średnicka-Tober et al. 2016).

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