This association was not found in men. The study evaluated the association between milk consumption and incident stroke in a healthy middle-aged Japanese population.
Milk consumption in Japan is lower than in Western countries. According to the National Health and Nutrition Survey in Japan in 2016, the average milk and dairy consumption was 111.2 g/day for adults and 306 g/day for children.
In the Netherlands, for example, mean dairy intake was between 321g to 374 g/day for adults and elderly, according to the Dutch National Food Consumption Survey 2012–2016.
Previous studies on milk and stroke risk have been inconsistent in Japan, mostly assessing mortality from stroke.
“To the best of our knowledge, this is the first prospective cohort study in Japan to investigate the association between milk intake frequency and the incidence of stroke,” researchers wrote in Nutrients.
Using data from the Iwate-Kenpoku cohort study which involved more than 17,000 subjects aged 40 to 69 years living in North East Japan, researchers narrowed to about 14,000 participants in this study.
Only healthy participants were included in this study, those who had history of stroke and CVD were excluded.
The study started in 2002 and participants were followed up for about 10 years. Blood pressure and other anthropometric data were also collected at the start.
A self-administered diet history questionnaire (BDHQ) was used to collect data on the frequency of milk consumption.
Based on their frequency, subjects were categorised into four groups, less than 2 cups/week, 2 to <7 cups/week, 7 to <12 cups/week and >12 cups/week.
For women, 43.1% consumed between 7 to <12 cups/week, followed by 2 to <7 cups/week (26.6%), 2 cups/week (13.9%) and >12 cups/week (16.4%).
Among men, most (35.5%) consumed between 7 to <12 cups/week. Only 12.8% consumed more than 12 cups/week.
During the follow-up, 478 stroke cases were detected. Stroke outcomes included total stroke, ischemic stroke and haemorrhagic stroke.
The results demonstrated that women who consumed milk at the frequency of 2 to <7 cups/week and 7 to <12 cups/week had a significantly lower risk of total and ischemic stroke compared with those who consumed <2 cups/week.
For haemorrhagic stroke, no significant association with milk intake frequency was observed.
In men, no significant associations were found between milk intake frequency and the risks of total stroke, ischemic stroke, and haemorrhagic stroke.
One factor for the differences between gender may be the “higher proportion of men with CVD risk factors, such as hypertension, diabetes, heavy drinking, and smoking habit, compared to women,” researchers said.
“These factors might have had a stronger impact on the incidence of stroke than the milk consumption, which might have masked the association between milk intake frequency and the incidence of stroke.
“Our findings suggest that moderate milk consumption (7 to <12 cups/week) decreased the risk of ischemic stroke in women but not in men. Consuming approximately 1 to <2 cups of milk/day may be effective in preventing ischemic stroke in the Japanese population.”
One thing the study did not cover was the mechanism between higher milk intake and lower stroke risk.
Although researchers think it might be due to the various minerals in milk such as potassium, calcium, and magnesium which have been shown to lower blood pressure levels.
“It has also been suggested that the proteins and peptides in milk may have antihypertensive and insulin secretion control effects.”
Since this study was conducted in Japan, the findings cannot be extrapolated to other regions especially the Western populations where milk consumption is much higher.
“However, we believe that our findings may be generalisable to the East Asian population, which share some common characteristics such as low milk intake, high salt intake, and relatively low levels of obesity with Japanese populations.”
This study was supported by the Japan Arteriosclerosis Prevention Fund, Japan Society for the Promotion of Science, Ministry of Health, Labor and Welfare, Health and Japan Dairy Association.
“Association between Milk Intake and Incident Stroke among Japanese Community Dwellers: The Iwate-KENCO Study”
Authors: Kozo Tanno, et al.