Motor neuron disease on the Kii Peninsula of Japan: excess manganese intake from food coupled with low magnesium in drinking water as a risk factor.

To identify important risk factors of motor neuron disease (MND) in a focus (Hohara) on the Kii peninsula of Japan, 24-h dietary duplicates, rice, drinking water, and soils were analysed for metals in Hohara and control areas. The manganese content in 24-h food in Hohara was significantly (P < 0.01) higher than that in the remote control areas. The incidence of MND in Hohara was well explained by the two parameters, manganese content in food and the magnesium concentration in drinking water (r2 = 0.99), suggesting that MND in this focus can be understood as a result of excess intake of manganese from food coupled with low intake of magnesium from drinking water. The reference to epidemiology and occupational medicine supports this conclusion. The crude annual MND incidence per 10(5) population in other foci may be predicted as MND = e alpha ln[beta(Mn in food)gamma/(Mg in water)], where alpha is 5.389-5.748, beta is 0.170-0.166, and gamma is 1.239-1.226.