The evidence indicates that dietary carotenoids, particularly lutein, zeaxanthin and β-carotene, are present in maternal serum, human milk, infant serum and in brain and retinal tissues. The researchers added that macular pigment optical density (MPOD), serum carotenoid levels and non-invasive skin measures serve as useful biomarkers for assessing carotenoid status. Other factors, including sources of carotenoids, sun exposure, co-intake of fats, and adiposity, also influence carotenoid levels in the body. As such, a longer duration of exclusive breastfeeding is linked to high skin carotenoid levels in later childhood, and the duration of breastfeeding had a significantly inverse association with body mass index. The role of carotenoids in visual milestone development has not been investigated with long-term controlled trials with nutrition and cognitive interventions.