This is the 306th most frequent Japanese word.
健康
Health.
Here, '健康' is used as a noun to describe the general state of being healthy.
彼女は毎日運動しているので、とても健康です。
She exercises every day, so she is very healthy.
In this context, '健康' functions as a noun referring to the general concept of health.
健康を維持するためには、バランスの取れた食事が重要です。
To maintain health, a balanced diet is crucial.
Here, '健康的な' is an adjective form of '健康,' meaning 'healthy,' qualifying the type of lifestyle.