How do I increase my baby's immune system? He is 6 months old and falls sick at least once a month.

1) Wonders of Breast Milk - Not only does it have undeniable nutritional value, it also provides infants with an added level of immune protection that no commercial formula has been able to duplicate. That’s because even colostrum—the first milk produced by new mothers—contains large numbers of antibodies and other infection-fighting cells. Through breast milk, nursing mothers are able to provide their babies with a continued source of antibodies long after they deliver. As a result, breastfed babies are protected against many if not all of the diseases to which their mothers’ are immune. 2) Sunshine! - Growing up in a tropical climate has its perks (minus the sweating and humidity) because when sunshine hits the skin, vitamin D is formed. Vitamin D is not only needed for the absorption of calcium to form healthy teeth and bone, it also contributes to a healthy immune system. Here in Sweden, during the dark dreary days, expat mothers from countries like Singapore and Thailand always lament about the sunshine factor. They end up having to feed their children with supplements instead else their children will fall sick easily.