Bell peppers and onions are both impressive sources of vitamin C. Vitamin C helps your body metabolize protein, contributes to the transmission of brain neurotransmitters and helps prevent infection. Healthy adults need between 75 and 90 milligrams of vitamin C each day. A half cup of [raw] green bell peppers adds 59.9 milligrams of vitamin C and a half cup of onions supplies 5.9 milligrams. A half cup of red bell peppers is even more impressive with 95.15 milligrams of vitamin C.
Bell peppers are a healthy source of vitamin A, a nutrient your body needs for healthy eyes, bones and cells. Vitamin A is also essential for the health of the linings of your respiratory, urinary and intestinal tracts. Healthy adults need between 2,310 and 3,000 international units of vitamin A each day to support these functions. A half cup of [raw] red bell peppers contains 2,332.5 international units and 1/2 cup of green bell peppers contains 275.5 international units.