Vitamin D is essential for modulating your immune system - to prevent HYPERACTIVITY (preventing allergic reactions such as sinusitis, hayfever and asthma) and also to help STIMULATE your PROTECTIVE immune cells - to ward of virus and bacterial infections. Despite the loads of sunshine we receive in Queensland, we are still a vitamin D deficient society possibly due to being overly 'sun safe'. Therefore supplementation may be warranted - 1000 - 2000 I.U. per day is usually sufficient however individuals will vary due to factors such as melanin content of skin, sun exposure and cholesterol levels. Vitamin D levels can be checked by your doctor and may be the key as to why you are suffering from constant recurrent infections or bogged down by allergies!!