ORIGINAL ARTICLE

Influence of years engaged in agriculture and number of pregnancies and deliveries on mortality of inhabitants of the Jinzu River basin area, Japan

E Kobayashi¹, Y Okubo¹, Y Suwazono¹, T Kido², M Nishijo³, H Nakagawa³, K Nogawa¹

¹ Department of Occupational and Environmental Medicine, Graduate School of Medicine, Chiba University, Japan
² Department of Community Health Nursing, Kanazawa University School of Health Sciences, Japan
³ Department of Public Health, Kanazawa Medical University, Japan

Correspondence to:
Correspondence to:
Dr E Kobayashi, Department of Occupational and Environmental Medicine, Graduate School of Medicine (A2), Chiba University, 1-8-1 Inohana, Chuohku, Chiba 260–8670, Japan;
etuko{at}med.m.chiba-u.ac.jp

Background: The occurrence of itai-itai disease is thought to be affected by such factors as pregnancy, lactation, hormonal disorders, aging, and calcium deficiency.

Aims: To study the influence of years engaged in agriculture and number of pregnancies and deliveries on the mortality of inhabitants of the Jinzu River basin area, which has been an endemic region for itai-itai disease.

Methods: From 6667 participants (3181 men, 3486 women; participation rate 93.4%) in the 1967 health survey, 3639 subjects (1591 men, 2048 women) whose years engaged in agriculture were established, and 2559 women/2410 women with a known number of pregnancies/deliveries were selected as the target population. These data were confirmed on the basis of self reported replies confirmed afterwards by interview. The survival survey was conducted for 6127 days from 1 August 1967 to 10 May 1984. Subjects were divided according to three water systems: the Jinzu River, non-Jinzu River, and mixed water system; the influence on mortality of the years engaged in agriculture and the number of pregnancies/deliveries was analysed using a Cox’s proportional hazards model according to the water systems.

Results: The mean years engaged in agriculture and mean number of pregnancies/deliveries were not different among the three water systems. Cox’s hazard ratios of these parameters to mortality were not statistically significant in the any of the water systems.

Conclusions: Neither the years engaged in agriculture nor the number of pregnancies/deliveries influenced mortality in subjects living not only in the non-Jinzu River basin but also in the Jinzu River basin using a Cox’s proportional hazards model.

Keywords: mortality; cadmium poisoning; pregnancy; delivery; itai-itai disease

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