expression, noun
root of all illness; source of all diseases
Proverbial expression often used in health advice to say that something (e.g., stress, poor diet) is the underlying cause of many illnesses.
ストレスは万病の元と言われる。
Stress is said to be the root of all illness.
睡眠不足は万病のもとです。
Lack of sleep is the source of all kinds of diseases.
A set phrase combining 万病 (all kinds of diseases) and 元 (source, origin). The exact origin is uncertain, but it reflects a traditional belief that many illnesses share a common root cause.