Newswise — In a paper just published electronically in the Journal of Alzheimer’s Disease, dramatic increases in Alzheimer’s disease (AD) in Japan and significant increases in developing countries are linked to changes in national diets.

The prevalence of AD for those aged 65+ years in Japan rose from 1% in 1985 to 7% in 2008. The prevalence of another major type of dementia, vascular dementia, was nearly constant at 4-5% during the same period.

Previous studies identified a number of risk factors for AD for which values in midlife or 15-30 years prior to diagnosis of AD are predictive: alcohol consumption, elevated cholesterol, diabetes mellitus, dietary fat, obesity, and smoking are associated with increased risk while physical fitness is associated with reduced risk.

In an effort to determine what might be the cause of this dramatic rise in AD prevalence, an investigation of dietary changes in Japan was undertaken. Data for dietary supply were obtained from the Food and Agriculture Organization of the United Nations. The largest changes between 1961 and 1985 included alcohol (from 29.6 kg/person/yr to 57.4 kg/person/yr), animal fat (from 5 kg/person/yr to 35 kg/person/yr), meat (from 7.6 kg/person/yr to 33.7 kg/person/yr), energy from animal products (from 249 kcal/person/d to 580 kcal/person/d), and rice (from 113 kg/person/yr to 69 kg/person/yr). In addition, lung cancer mortality rates for those over the age of 60 years increased from 69 deaths/100,000/yr for males and 22 deaths/100,000/yr for females in 1961 to 213 deaths/100,000/yr for males and 54 deaths/100,000/yr for females. Values for most of these factors have changed only modestly since 1985.

The dietary consumption data for various years (e.g., every 5 years from 0 to 25 years before AD prevalence data) were examined statistically for their correlation with AD prevalence in Japan. Correlation coefficients of about 90% were found, with maximum values for alcohol, animal product energy, lung cancer, meat, and rice generally occurring with a lag of 15 to 25 years.

The mechanisms linking animal products and meat to risk of AD include iron from meat, which increases oxidative stress, and arachidonic acid from meat, which can increase inflammation in the brain, and cholesterol from all animal products.

Thus, this study suggests that the nutrition transition in Japan, i.e., switching from the traditional Japanese diet with 15% of the energy derived from animal products and 42% from rice towards the Western diet, is associated with the rapid rise in AD prevalence in Japan. Since the dietary supply factors have not changed appreciably since 1985, it may be the case that AD prevalence rates in Japan have reached a peak and will not increase further. In addition, unless the dietary pattern in Japan returns to the traditional Japanese diet, AD rates in Japan will not decrease.

A second study reported in this paper was of AD prevalence for those over the age of 65 years in eight developing countries: Brazil, China, Cuba, Egypt, India, Nigeria, Republic of Korea, and Sri Lanka. AD prevalence ranged from 1.3% in India to 8.0% in the Republic of Korea. The prevalence data were from different years ranging from 1995 for Nigeria to 2005 for Brazil and China. The dietary supply factor with the highest correlation with AD was total energy (calories), which had a correlation coefficient of 0.87 for lags of 20 and 25 years between the dietary supply values and AD prevalence. Total energy is associated with overweight and obesity, which are associated with risk of AD.

The important message from this study is that AD rates globally are strongly linked to diet, especially in midlife, and that unless per capita consumption of animal products and total energy is reduced, AD rates will continue to remain high.

Dr. Hiroko Dodge, Associate Professor of Neurology at Oregon Health & Science University (Portland, OR, USA), who published the paper with the data on Alzheimer's disease prevalence in Japan used in this study, agrees that diet plays an important role in the risk of Alzheimer's disease. She commented as follows: “Dr. Grant’s study is important and also unique in the way that he examined the association between AD prevalence and national dietary patterns observed various years before the AD prevalence studies were conducted. His study suggests that national dietary patterns when subjects were in their midlife are highly correlated with prevalence of AD later on when subjects reach 70 years and older. Since there are no definitive pharmacological cures for AD yet, it is very important to prevent or delay the onset of AD. If we all pay attention to what we eat and do at least moderate exercise, we can significantly reduce societal burden of dementia in the future”.

According to George Perry, Ph.D., Editor of the Journal of Alzheimer’s Disease, “Dr. Grant has been at the forefront of studies linking Alzheimer disease to diet, beginning in 1997 with articles in the Journal of Alzheimer’s Disease and elsewhere.”

“Directly linking increased Alzheimer’s disease to diet changes in Japan strengthens the case for lifestyle playing as much a role in Alzheimer’s as it does in most age-related degenerative diseases.”