July 28, 2015

Is milk bad for you?

EVERYTHING seems to be bad for you if you read enough in the health literature, but milk would seem pretty safe.  "New Scientist" has however just done a big article pointing out various doubts about milk.  They don't however have much in the way of actual scientific evidence against milk.  The one academic journal article they cite is below:

Milk intake and risk of mortality and fractures in women and men: cohort studies

Abstract

Objective: To examine whether high milk consumption is associated with mortality and fractures in women and men.

Participants: Two large Swedish cohorts, one with 61?433 women (39-74 years at baseline 1987-90) and one with 45?339 men (45-79 years at baseline 1997), were administered food frequency questionnaires. The women responded to a second food frequency questionnaire in 1997.

Main outcome measure: Multivariable survival models were applied to determine the association between milk consumption and time to mortality or fracture.

Results: During a mean follow-up of 20.1 years, 15?541 women died and 17?252 had a fracture, of whom 4259 had a hip fracture. In the male cohort with a mean follow-up of 11.2 years, 10?112 men died and 5066 had a fracture, with 1166 hip fracture cases. In women the adjusted mortality hazard ratio for three or more glasses of milk a day compared with less than one glass a day was 1.93 (95% confidence interval 1.80 to 2.06). For every glass of milk, the adjusted hazard ratio of all cause mortality was 1.15 (1.13 to 1.17) in women and 1.03 (1.01 to 1.04) in men. For every glass of milk in women no reduction was observed in fracture risk with higher milk consumption for any fracture (1.02, 1.00 to 1.04) or for hip fracture (1.09, 1.05 to 1.13). The corresponding adjusted hazard ratios in men were 1.01 (0.99 to 1.03) and 1.03 (0.99 to 1.07). In subsamples of two additional cohorts, one in males and one in females, a positive association was seen between milk intake and both urine 8-iso-PGF2? (a biomarker of oxidative stress) and serum interleukin 6 (a main inflammatory biomarker).

Conclusions: 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. Given the observational study designs with the inherent possibility of residual confounding and reverse causation phenomena, a cautious interpretation of the results is recommended.

SOURCE

This is very weak evidence of anything, as the authors admit in their final sentence.  Let me spell it out:  The milk-consumption data is from a self-report questionnaire rather than any actual observations or  measurements -- and such data is notoriously subject to social desirability influences, among other distortions.  

There are two possibilities:  1). Sickly people drink a lot of milk in the belief that it is good for them; 2). Sickly people SAY they drink a lot of milk in the belief that they SHOULD do that.  Either way the sickliness probably came first, not the milk drinking.  So sickliness caused milk drinking rather than milk drinking caused sickliness.  It could go either way and we do not know which way. The study, in other words, did not advance our knowledge of the matter at all.  There is still no reason to think that milk is bad for you.





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