So about the best thing you can do is lose weight, get your BMI below 20, increase aerobic exercise, and get out in the sunshine a lot. And maybe take Vit C, Vit D, Zinc, NAC, and Quercitin supplements.
BMI does not differentiate between muscle and fat. A person who is very healthy could have a BMI that is considered “obese.”
FWIW-
A BMI below 20 is not healthy and leaves little reserve. An optimal BMI is between 20 and 25