Table 2.

Clinical studies of vitamins A, C, E, and D.

Vitamins	Cancer type	Sample size	Study type	Type of vitamins and doses	The outcome of the study	References
Vitamin A	Acute promyelocytic leukemia	235	A randomized, controlled, open-label multicenter trial, phase 3 trial	All-trans retinoic acid (45 mg/m2)	Using all-trans retinoic acid with arsenic acid has increased the cure rate and reduced relapse chances	(140)
	Gestational trophoblastic neoplasia	32	A randomized, controlled clinical trial	oral vitamin A (6,000 IU/day)	The intervention group exhibited a reduction of chemoresistance as well as a downregulation of the tumor marker β-hCG level	(141)
	Advanced cervical carcinoma	30	A randomized double-blind study	Vitamin A supplementation (8,000 IU/8 h)	Improved therapeutic response of the chemotherapy	(142)
Vitamin C	Advanced-stage non-small cell lung cancer	38	Open-label, single-arm, non-randomized phase II study	Ascorbate (75 g twice per week) intravenously	Improved tumor deterioration and enhance immune response	(148)
	Metastatic colorectal cancer or gastric cancer	36	Phase 1 open-label, single-center, dose-escalation, and speed-expansion study	Ascorbic acid (0.2–1.5 g/kg) infusion	Improved therapeutic response of the chemotherapy and significantly decreased the side effects	(149)
Vitamin E	Thyroid carcinoma	89	A randomized, controlled clinical trial	NA	The results revealed the protective impact of vitamin E on salivary glands by enhancing parotid excretion function	(150)
	Prostate cancer	154	A randomized, placebo-controlled, double-blinded clinical trial	Vitamin E (400 IU/day)	Significantly decreased serum C22 lactone sulfate which is highly associated with modulating androgenic steroid metabolites	(151)
Vitamin D	non-small-cell lung cancer	155	A randomized, double-blind, placebo-controlled, parallel group trial	Vitamin D supplements (1,200 IU/day)	Patients with lower 25(OH)D levels who have early-stage lung adenocarcinoma may have a better chance of surviving if they take vitamin D supplements.	(153)