If you are over 18 years old & your vitamin D blood level is under 30ng/ml, ask your doctor if you can take 8,000IUs to 10,000IUs of safe over-the-counter Vitamin D3 DAILY, and 50,000IUs of safe Vitamin D3 (not D2) twice a week for 2 to 4 weeks to boost levels. Get a nutrient blood test to find other deficiencies that harm immune systems like Vitamins A, B1, B6, C, D, E, & minerals magnesium, iron, copper, selenium & zinc. If you are 18 or younger, ask a Doctor who knows D3 dosing to help you get over 30ng/ml. Target a 25(OH)D blood level of 50 to 80ng/ml.