Whitebeard was not healthy at marine fold and his health deteriorating without his machines he was hooked into:
Crocodile called him weak compared to what he was before:
Whitebeard knew about all of this and even admitted it to himself that he cant be the strongest for ever and that hes becoming weaker and that he has one heart implying that he knew that the disease is affecting his health very badly and that if he can save ace he will be competent with what he did:
Whitebeard was hooked to machines and when he was unhooked of the medicine and his crew showed that the were concerned of his health being unhooked. Oda himself said that these medicine were there to help him live basically because without them his condition can not be stable, These are the authors words himself from an sbs:
Conclusion : MarineFold White beard was dying and very far off from his Prime. Which means he could have just died off without his medicine at any point being. He was not just sick. He needed medicine to even stay alive.