Α-Carotene

α-Carotene (alpha-carotene) is a form of carotene with a β-ionone ring at one end and an α-ionone ring at the opposite end. It is the second most common form of carotene.

Human physiology
In American and Chinese adults, the mean concentration of serum α-carotene was 4.71 μg/dL. Including 4.22 μg/dL among men and 5.31 μg/dL among women.

Dietary sources
The following vegetables are rich in alpha-carotene:
 * Yellow-orange vegetables: Carrots (the main source for U.S. adults), sweet potatoes, pumpkin, winter squash
 * Dark-green vegetables: Broccoli, green beans, green peas, spinach, turnip greens, collards, leaf lettuce, avocado

Research
A 2018 meta-analysis found that both dietary and circulating α-carotene are associated with a lower risk of all-cause mortality. The highest circulating α-carotene category, compared to the lowest, correlated with a 32% reduction in the risk of all-cause mortality, while increased dietary α-carotene intake was linked to a 21% decrease in the risk of all-cause mortality.