TABLE 4.

Potential future research objectives

Retinol-binding protein 4	Establish if observed associations are causal
	Establish if effects occur independently of vitamin A metabolism at large
Retinol	Establish if disease associations observed for serum retinol are present for more sensitive markers of vitamin A status, including retinol isotope dilution
	Replicate findings that retinol can interact with other risk factors, and establish if interactions occur independently of confounders, particularly inflammation
	Establish whether deficient vitamin A status contributes to the growing burden of lifestyle diseases in low- to middle-income countries
Retinoic acid	Evidence on the link between retinoic acid and major lifestyle diseases is lacking. More studies are needed in order to establish associations
	Establish standardized methods that accurately capture retinoic acid concentrations
	Establish clinical relevance