What do systematic reviews say?

Oral vs intramuscular vitamin B12

• Oral vitamin B₁₂ versus intramuscular vitamin B₁₂ for vitamin B₁₂ deficiency 2018 · Cochrane Headline outcomes only
  no estimate extracted
  2 studies · 120 participants
  Very low

Summary of findings: oral vitamin E supplementation vs placebo or no treatment

Summary of findings: oral vitamin E supplementation showed no clear difference in adverse events compared with placebo or no treatment (low certainty).

• Antioxidant supplementation for lung disease in cystic fibrosis 2019 · Cochrane Headline outcomes only
  OR 1 [0.13, 7.94]
  1 study · 38 participants
  Low

Oral nutritional supplements vs placebo

It is very uncertain whether oral nutritional supplement with 20 g protein per 200 mL bottle, 1… changes adverse events (death) compared with placebo (very low certainty).

• Nutritional interventions for treating foot ulcers in people with diabetes 2020 · Cochrane Headline outcomes only
  RR 0.96 [0.06, 14.6]
  1 study · 53 participants
  Very low

Vitamin A vs placebo

• Oral vitamin A supplements to prevent acute upper respiratory tract infections in children up to seven years of age 2024 · Cochrane Headline outcomes only
  no estimate extracted
  1 study · 116 participants
  Very low