乙醛是有毒物质，会损害人体的DNA。

Acetaldehyde is toxic and has been shown to damage DNA.

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这会损害人体的免疫系统，引起其他健康问题。

This leads to a weakening of the body’s immune system, and ends up causing other health problems.

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许多研究显示，悲观主义者的无助感会损害人体的自然防御体系，即免疫系统。

Many studies suggest that the pessimist's feeling of helplessness undermines the body's natural defenses, the immune system.

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