Asian Scientist (Oct. 3, 2013) – A dramatic increase in Japan’s Alzheimer’s disease (AD) incidence since the 1980’s may be associated with a change from the traditional Japanese diet towards a Western one, according to a new study.
The prevalence of AD for those aged 65+ years in Japan rose from 1% in 1985 to 7% in 2008 while the prevalence of another major type of dementia, vascular dementia, remained nearly constant at 4-5% during the same period.
Although previous studies had identified a number of risk factors for AD, including alcohol consumption, elevated cholesterol, dietary fat, obesity, and smoking, it was not clear if diet had contributed to this dramatic rise in AD prevalence in Japan.
To determine possible causes of this rise in AD prevalence, researchers undertook an investigation of dietary changes in Japan over this period.
In the study, published in the Journal of Alzeimer’s Disease, the researchers analyzed data for dietary supply from the Food and Agriculture Organization of the United Nations.
They found significant dietary changes in Japan between 1961 and 1985 that included large increases in alcohol, animal fat, meat, and animal product consumption. In particular, meat and animal product consumption rose by 7 and 4 fold, respectively, while rice consumption was cut almost in half. Values for most of these factors have changed only modestly since 1985.
The researchers found that these dietary changes were significantly correlated with the increase in AD prevalence, with a lag of between 15 to 20 years.
This suggests that the nutrition transition in Japan, i.e., switching from the traditional Japanese diet (where energy is derived mainly from rice) towards the Western diet (where a high percentage of energy is derived from meat and animal products) may have caused the rapid rise in AD prevalence in Japan.
Animal products and meat are known to increase the risk of AD because they contain compounds such as iron and arachidonic acid that have been shown to increase oxidative stress and inflammation in the brain, respectively.
Since diets have not changed appreciably in Japan since 1985, it is possible that AD prevalence rates in Japan may have reached a peak and will not increase further. However, unless Japanese people return to the traditional Japanese diet, AD rates in Japan are unlikely to decrease.
The article can be found at: Grant (2013) Trends In Diet And Alzheimer’s Disease During The Nutrition Transition In Japan And Developing Countries.
Source: Grant Array Associates Health Research; Photo: DrHobo/Flickr/CC.
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