I agree dental health is one important factor in immune strength. Do not overlook any dental problems. When symptoms appear, don't dismiss them. Bleeding, soreness, or sensitivity. Don't ever think oh it's just my teeth, I can live with it. Dental infections, even the non painful kind, will knock you down fast by lowering your immune system and then whamo you feel bad all the time. It takes a long time for your body to fight off anything if your immune system is weak.