Researchers from Columbia University identified 29 studies looking at carotenoid exposure and sleep, including 11 human intervention trials. Nine of these reported improvement in at least one sleep-related outcome, although the effects were not consistently significant compared with placebo
“Emerging evidence suggests that greater carotenoid intake may be associated with more favorable outcomes across multiple dimensions of sleep health,” the researchers wrote in Nutrients
They added that the evidence from intervention studies remained “insufficient to recommend specific carotenoids, doses, or supplementation strategies for improving sleep.”
The 11 intervention studies covered a fairly broad mix of carotenoids, doses and populations, making it difficult to draw conclusions about any one ingredient
Lutein and zeaxanthin were among the better studied. In one 6-month trial, a combination of lutein, zeaxanthin and meso-zeaxanthin improved sleep quality compared with placebo after three and six months. An 8-month study of lutein and zeaxanthin also reported improvements in sleep duration, nighttime awakenings and relaxation upon waking
Those findings were tempered by another 6-month trial in which sleep-related impairment improved with lutein and zeaxanthin, but also improved in the placebo group
There were also some notable results for crocin and crocetin, apocarotenoids found in saffron
Purified crocin at 30 mg/day improved sleep quality compared with placebo after eight weeks in men receiving methadone maintenance treatment. Two small crocetin trials found fewer wake episodes and changes in objective sleep measures, respectively
Astaxanthin and fucoxanthin showed improvements in some measures from baseline, but without clear overall differences from placebo, and β-cryptoxanthin did not significantly affect sleep quality or duration
“Across intervention studies, improvements were observed for some sleep-related outcomes relative to baseline or placebo; however, findings were not consistent across outcomes or carotenoid interventions,” the researchers wrote
The intervention findings sit alongside observational evidence linking carotenoid status with sleep
Across 14 observational studies, higher dietary intake or serum concentrations generally tracked with more favorable measures of sleep quality and duration. One study reported 71% and 81% lower odds of poor sleep quality among people in the third and fourth quartiles of total carotenoid intake, respectively, compared with the lowest quartile
The relationship could involve the antioxidant and anti-inflammatory properties of carotenoids. Sleep deprivation and circadian disruption have both been linked to oxidative stress and inflammation, giving the researchers a potential mechanistic link between carotenoid intake and sleep
But that mechanism has not been demonstrated in humans, and the review pointed to a basic problem with the evidence so far: the studies were looking at different carotenoids, in different populations, at different doses and using different definitions of sleep outcomes
All 11 human intervention studies also tested supplements, leaving the effects of carotenoids consumed through food largely unexplored
The researchers said future work should establish dose–response relationships for individual carotenoids and use standardized subjective and objective measures of sleep
“Carotenoid-rich foods may continue to be encouraged within existing healthful diet recommendations but should not be specifically prescribed as a strategy to improve sleep until efficacy is established,” they concluded
