In a study published earlier this month, Swedish researchers concluded that large volumes of milk could promote chronic low-grade inflammation in the body.
However, the study went further with the insinuation that there was a heightened risk based on gender.
“The present study repeats the results of the original paper, in terms of milk and mortality, and repeats the same hypothesis, in terms of galactose,” said Dr Anne Mullen, director of Nutrition at the Dairy Council.
"The result on mortality has been critiqued, assessed as an outlier and the effect is neutralised when incorporated into more powerful meta-analysis; the hypothesis on galactose remains poorly supported."
Lead author of the study Dr Karl Michaëlsson, professor of Medical Epidemiology at Uppsala University, responded to the criticism by pointing out that providing galactose to research animals was an established aging research model, with a mechanism of increased oxidative stress and inflammation.
“The amount of galactose provided to these animals corresponds to 1-2 glasses of milk. In addition, female animals are more vulnerable than male animals,” he said.
“A sex difference in sensitivity of galactose exposure has been identified experimentally and the galactose elimination capacity is also higher in males than in females.”
“Yes, our study might be considered as an outlier in the sense that it is very large with a wide exposure range in milk consumption with many people who drink a lot of milk and many who drink modest amounts of milk,” he continued.
“We specifically considered non-fermented and fermented milk consumption separately. We also had time-updated information in women and, finally we had NO loss to follow-up and high number of outcomes.
Fruit and veg counteraction
The study also found evidence that an adequate fruit and vegetable intake could provide a degree of protection from the oxidative and inflammation processes caused by galactose supplementation.
“Our present study partly supported this case,” said Dr Michaëlsson. “Milk may induce inflammation and oxidative stress, potentially via galactose.
“Therefore, we disagree that our hypothesis is far-fetched.”
Dr Michaelsson’s 2014 study took on a similar note, with investigations looking into high milk consumption and its links to mortality and fractures in women and men.
His team found that high milk intake was associated with higher mortality in one cohort of women and in another cohort of men, and with higher fracture incidence in women.
At the time the Michaëlsson group recommended a cautious interpretation of the results due to its observational study design and a possibility of residual confounding and reverse causation phenomena.
However, that didn’t stop the research and its team being subject to much scepticism by researchers such as Dr Arne Astrup and Dr Ian Givens.
'Confusing message about dairy'
Writing in the British Medical Journal soon after the publication of Dr Michaëlsson’s study the researchers questioned the findings obtained from two Swedish population cohorts that used self-reported information about dietary intakes.
Drs Astrup and Givens referred to other studies that also used both cohorts but had a shorter follow-up and smaller cohort size.
Findings here revealed significantly lower risk of major cardiovascular disease (CVD) and cancers than for those who consumed higher amounts of dairy, and with no indication of any possible increased risk for high milk intakes.
The two authors also questioned the validity of self-reported information about dietary intake as a problem in population studies possibly leading to false conclusions.
“The most likely explanation for the findings are that the authors have in reality studied, not the effect of high dairy intakes, but the results of being obese,” they claimed.
“Under-reporting of body weight among the overweight and particularly obese individuals, would mean that the true BMI across the quintiles would be increasing, and that total energy intake, and intakes of most foods would go up.
“An increased BMI causes an increased mortality due to both cancer and CVD.”
Dr Michaëlsson responded by pointing out that on average, in both cohort studies and in randomised clinical trials - despite a higher energy intake - no weight gain has been observed with high dairy consumption.
“Let us also remind the reader that a higher energy intake also was found among high consumers of fermented milk products in our BMJ (2014) study but mortality rates were lower, in contrast to the findings in those with high non-fermented milk consumption.”