Table 1. Clinical efficacy.

Author	Groups studied and intervention	Results and findings	Conclusions
Study 1: Amaeze et al. [19]	A randomized placebo-controlled trial assessed the changes in CYP2D6 and CYP3A activities throughout pregnancy and studied the effect of vitamin A on CYP2D6.	The Dextrorphan (DX)/ 3-hydroxymophinan (3HM)/ Dextromethorphan (DM) urine ratios used to assess increased CYP3A and CYP2D6 activity were significantly higher during pregnancy compared to post-partum. Vitamin A supplements did not change CYP2D6 activity however plasma all-trans retinoic acid concentrations positively correlated with increased CYP2D6 activity during pregnancy and postpartum.	Further research should be done to look at the mechanism of increased CYP2D6 activity during pregnancy.
Study 2: Ding et al. [20]	A randomized placebo-controlled trial evaluated the effects of daily oral low-dose vitamin A supplementation in lactating mothers and the health status of infants in China.	While maternal serum retinol concentration is usually expected to drop during breastfeeding, the decrease in the supplemented group had a significantly lower drop than in the control group. Additionally, maternal serum retinol concentrations were shown to increase in the supplementation group, with no change observed in the control group. Infant febrile illness, respiratory tract infections, diarrhea, and eczema showed no difference between the two groups despite vitamin A supplementation.	Daily oral vitamin A supplementation helps improve vitamin A status. However, there was no effect on infant health status through breast milk.
Study 3: Nga et al. [22]	A randomized controlled trial assessed the effects of a nutrient-rich, food-based supplement given to rural Vietnamese mothers before and/or during pregnancy on birth outcomes.	The food-based supplement given from pre-conception to term or mid-gestation to term increased protein, iron, zinc, folate, vitamin A, and B12 intakes; however, it failed to alter infant measurements such as height and weight, at birth.	A nutrient-rich, food-based supplement did not affect maternal or infant outcomes.
Study 4: Hidayat et al. [23]	A randomized clinical trial to evaluate b-hCG levels in low-risk gestational trophoblastic neoplasia (GTN) patients after vitamin A administration.	Compared to control groups, levels of b-hCG and incidence of chemotherapy resistance were found to be lower for patients with low-risk GTN who underwent methotrexate chemotherapy.	For low-risk GTN patients undergoing methotrexate chemotherapy, an oral dose of 6,000 IU of vitamin A given orally could help to reduce b-hCG levels.
Study 5: Palmer et al. [24]	A cluster-randomized study focusing on how nutritional content i.e., vitamin A or β-carotene affects thymus phenotype during prenatal and childhood in rural Nepal.	There is a positive correlation between gestational age at delivery and higher thymulin concentrations among children born to β-carotene-supplemented mothers. Height and weight of children between the ages of 9-12 years showed a positive correlation to thymulin concentrations as well. Seasonal decreases in thymulin levels were observed during pre-monsoon, monsoon, and pre-harvest relative to the post-harvest season.	Findings give a baseline on how nutritional content affects the phenotyping of the thymus in prenatal and adolescence. The potential disease risk of undernutrition could also affect the role of thymulin in the neuroendocrine regulation of inflammation, but this has yet to be explored.
Study 6: Haskell et al. [21]	Two randomized trials assess small-quantity, lipid-based nutrient effects on plasma or milk retinol concentration among young Malawian or Ghanaian children.	Plasma retinol concentrations and milk retinol concentrations in Malawian mothers did not change between the groups that received iron and folic acid supplements, multiple micronutrients, and small-quantity lipid-based nutrient supplements. A similar result was found in Malawian children and Ghanaian children.	Small-quantity lipid-based nutrient supplements have no effect on vitamin A levels in Malawian mothers and Malawian and Ghanaian children.