Mortality risk and beta-carotene from food vs. supplements:
The studies mentioned suggest a lower risk of mortality stems from beta-carotene intake from food sources rather than supplements which provides evidence that other phytonutrients contained in the food sources are translating to the benefits. It is also possible that high levels increase mortality. A similar effect is seen when vitamin D levels become high which results in an increased mortality rate. The benefit may also come from other substances in the vegetable food source and not necessarily the beta carotene itself.
Beta-carotene supplements:
A review and meta-analysis of 6 randomized controlled trials including 40,544 patients found no benefit of non-food beta-carotene supplementation on risk of cancer or cancer mortality. These results were confirmed in other primary and secondary prevention trials. Other analyses found that beta-carotene supplementation significantly increased the risk of urothelial cancer (cancer of the layer that lines the urinary tract, the bladder, and parts of the urethra), especially bladder cancer by 52%. Among current smokers, it also increased the risk of cancer by 7%. (13)