Dairy

In a 2020 study of Chinese people living in Singapore,¹ Talaei et al. found that those who ate more dairy foods had better cognitive function, and study participants who drank milk every day were 14% less likely to be categorized as cognitively impaired on the SM-MMSE test they used to assess them.  In contrast, Muñoz-Garach et al.² found that overweight Spanish participants with metabolic syndrome in their 2021 study who ate more dairy foods scored worse on their MMSE test, and that dairy intake resulted in 10% greater likelihood of cognitive impairment.  Both studies used food-frequency questionnaires to document the normal diet of their participants. 

In the Talaei et al.¹ study, 65% of participants drank milk less than once a month.  Half of the participants consumed less than 28.7 grams of dairy products per day.  The median intake of dairy products among the quartile of participants who consumed the most dairy products and scored the best on the cognitive test was 252 grams per day.  In the Muñoz-Garach et al.² study, those participants who scored the best were those who ate on average less than 220 grams per day of dairy products.  Those who scored the worst were eating on average more than 395 grams of dairy foods per day.  It seems to me that the groups who scored the best in each of the two studies were actually eating similar amounts of dairy products to each other, so perhaps it is not a matter of dairy being simply either beneficial or detrimental to cognitive health, but rather that in moderation it may be beneficial, while also detrimental in excess.  Muñoz-Garach et al.² reference numerous studies and note that some found intake of dairy to be associated with good cognition, while others found the inverse. 

An additional finding of the Muñoz-Garach et al.² study was that their participants who ate more full fat dairy scored better on the cognition test, while those who drank more skim milk scored worse; full fat dairy was not associated with cognitive impairment.  They reference other studies that found dairy fat to be beneficial for people with diabetes and metabolic syndrome, which they note could be risk factors for cognitive impairment. 

In deciding how much milk and dairy I want to consume every day, I would want to look at more than just these two studies.  Moderation is a good starting point, but I also need to decide whether to drink whole milk or skim milk, homogenized or unhomogenized, organic or local, pasteurized or raw.  This comparison of two studies is a reminder to look beyond the title of the study, to look for results to be replicated in different populations, and to consider whether there are characteristics of the food you have available to you that may be different from what was used in the study.  Plus everyone has their own biochemical individuality, so a food that’s great for one person might not be great for another person, or even for the same person at a different point in time along their health journey.

References

1. Talaei M, Feng L, Yuan J-M, Pan A, Koh W-P. Dairy, soy, and calcium consumption and risk of cognitive impairment: the Singapore Chinese Health Study. European Journal of Nutrition. 2020;59(4):1541-1552.
2. Muñoz-Garach A, Cornejo-Pareja I, Martínez-González MÁ, et al. Milk and Dairy Products Intake Is Related to Cognitive Impairment at Baseline in Predimed Plus Trial. Mol Nutr Food Res. 2021;65(7):e2000728.