Multivitamins works for me... I always use this brand.. Berroca by Bayer and Mutlivitamin caplets... Always always hydrate yourself with plenty of water .. Cut down smoking if possible & plenty of rest ...
IMHO Divers are prone to sickness due to long travel, extreme weather.... Your body will have less immunity if you are lack of rest & tired
As a dive instructor.... DCS always a risk... always go up and down