Hormonal
High-dose supplementation of fat-soluble vitamins (specifically Vitamin E and beta-carotene) and Vitamin A in well-nourished adults increases the risk of adverse health outcomes, including bleeding, cancer recurrence, and all-cause mortality, rather than providing preventive health benefits.
Do not assume high-dose fat-soluble vitamin supplements (A, E) are safe just because they are vitamins. In well-nourished adults, high doses (e.g., Vitamin E >800mg/day, Beta-carotene in smokers) are linked to increased risks of bleeding, cancer recurrence, and mortality. Stick to dietary sources or standard multivitamins unless a deficiency is diagnosed by a physician.
Toxicity following consumption of water-soluble vitamins is rare. However, photosensitivity and neurotoxicity have been reported at doses higher than 500 mg/day of pyridoxine (vitamin B6)... Reports of toxicity associated with overconsumption of supplemental antioxidant fat-soluble vitamins are more prevalent. Vitamin E... doses of 800–1,200 mg/day can result in bleeding... doses above 1,200 mg/day can result in diarrhea, weakness, blurred vision, and gonadal dysfunction... vitamin E supplementation following radiation therapy... was associated with increased cancer recurrence... meta-analysis has suggested an increase in all-cause mortality after high-dose vitamin E supplementation... male smokers receiving β-carotene supplements had significantly increased the risk of lung cancer... Excess vitamin A supplementation has been suggested to be associated with adverse effects on bone health... increased incidence of congenital abnormalities
Why this rating
The paper cites large clinical trials (ATBC, Retinol Efficacy Trial), meta-analyses, and randomized trials, indicating strong evidence for specific high-dose toxicities, though general multivitamin safety is described as having 'limited evidence' of benefit.
Source
Adverse Effects of Nutraceuticals and Dietary Supplements
Martin J. J. Ronis et al. · The Annual Review of Pharmacology and Toxicology · 2017
DOI 10.1146/annurev-pharmtox-010617-052844
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