I suffer from allergies and asthma. I started taking 2,000 IU of vitamin D daily several months ago. I am also taking turmeric capsules.
This spring I have had no allergies, sinus infections and asthma problems. Perhaps these supplements are keeping my immune system from overreacting to pollen.
In animal studies, turmeric prevents the release of histamine from mast cells (Molecular Nutrition and Food Research, September 2008). If it works similarly in humans, this would prevent allergy symptoms from developing.
Vitamin D has anti-inflammatory effects on smooth muscle cells in the airways (British Journal of Pharmacology, September 2008). This might help counteract asthma.