Table 2.

Overall risk of bias by supplement. N represents the total number of studies for each supplement.

Supplement	Overall Risk of Bias
Vitamin C (n = 5)	Low: 4 (80%) Some concerns: 1 (20%) High: 0 (0%)
Vitamin D (n = 29)	Low: 25 (86.2%) Some concerns: 3 (10.3%) High: 1 (3.4%)
Vitamin E (n = 7)	Low: 6 (85.7%) Some concerns: 0 (0%) High: 1 (14.3%)
Calcium (n = 21)	Low: 17 (81.0%) Some concerns: 2 (9.5%) High: 2 (9.5%)
Magnesium (n = 18)	Low: 17 (94.4%) Some concerns: 1 (5.6%) High: 0 (0%)
Potassium (n = 12)	Low: 9 (75%) Some concerns: 2 (16.7%) High: 1 (8.3%)

The number of studies obtaining each of the three grades is noted in Column 2, with the percentages reflecting the frequency of each assignment for each supplement.