In the past,why was the prevalence of chronic disease so low?

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In the past, infectious diseases such as tuberculosis, cholera, smallpox, and influenza were widespread and often fatal. Many people did not live long enough to develop chronic diseases such as heart disease, diabetes, and cancer. With improvements in hygiene, sanitation, and medical care, infectious diseases have become less prevalent, allowing people to live longer, but also increasing the risk of developing chronic diseases.

In the Past,why Was the Prevalence of Chronic Disease So