He ruined his health by working too hard.

He worked too hard, and became sick.

He worked so hard that he ruined his health.

He worked so hard that eventually he made himself ill.

Don't work too hard.

Working to excess will do you harm.

Don't work yourself sick.

It won't be wise to overwork at the cost of your health.

You had better not work too hard.

We cannot work too hard.