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Supplements BODY HANDBOOK
Supplements · §558
Vitamin A
Vitamin A is one of the few where "eat more" is the wrong instinct. It comes two ways: preformed retinol from liver, eggs, and dairy, which your body uses straight; and beta-carotene from orange and dark-green plants, which your gut converts as needed. For most well-fed adults, food covers it and a supplement does almost nothing good. What matters is knowing the three narrow lanes where this vitamin bites: pregnancy, smoking, and quietly stacked doses. Stay clear of those and you can forget about it.
Do · As-needed Evidence Strong Chapter Supplements

Too little kills children; too much harms Western adults. In deficient regions, two high-dose capsules a year cut all-cause child death by about a tenth 1. But on a Western diet the strong signals run the other way.

Pregnancy: more than 10,000 IU a day of preformed retinol in early pregnancy carried nearly five times the risk of cranial and facial birth defects 2.

Smokers: high-dose beta-carotene pills raised lung cancer risk by roughly a fifth, and the USPSTF now recommends against them 3 4.

Bones: the highest retinol intakes, easy to hit with daily liver or stacked pills, roughly doubled hip-fracture risk 5.

The catch is that retinol is fat-soluble and banked in your liver, so excess doesn't flush out; it accumulates. The daily upper limit is only about three times the daily need 6. Beta-carotene from food has no ceiling, because the gut throttles its own conversion once retinol is plentiful.

Check yourself against the three lanes, then stop thinking about it.

The fine print — when to skip it, and what people get wrong

"Carrots sharpen your eyesight." They cure night blindness from deficiency; they don't improve normal vision. The myth is WWII British propaganda that hid the RAF's new radar, and it stuck for eighty years.

"Eat more vitamin A for clearer skin." The wrinkle and acne effects come from retinoid creams on your face, not your dinner 8.

"It's a vitamin, you can't overdose." You can: chronic excess causes hair loss, dry skin, headaches, and at the far end liver and bone damage.

Nobody chooses toxicity; they stack into it. A multivitamin, cod liver oil for omega-3s, and weekly liver each look modest but can total 20,000–30,000 IU a day, the bone-fracture zone 9. Hair loss is often the first sign; the bone cost is silent until a fracture.

Chronic liver disease lowers the toxicity threshold; ask your hepatologist before supplementing. Oral prescription retinoids (isotretinoin, acitretin) are separate clinical territory, not this dietary advice.

References
  1. 1Imdad A, Mayo-Wilson E, Haykal MR et al. (2022). Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age. Cochrane Database of Systematic Reviews. link
  2. 2Rothman KJ, Moore LL, Singer MR et al. (1995). Teratogenicity of high vitamin A intake. New England Journal of Medicine. link
  3. 3The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group (1994). The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. New England Journal of Medicine. link
  4. 4USPSTF (2022). Vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer: US Preventive Services Task Force recommendation statement. JAMA. link
  5. 5Michaëlsson K, Lithell H, Vessby B, Melhus H (2003). Serum retinol levels and the risk of fracture. New England Journal of Medicine. link
  6. 6Institute of Medicine (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. link
  7. 7Lietz G, Oxley A, Leung W, Hesketh J (2012). Single nucleotide polymorphisms upstream from the β-carotene 15,15'-monoxygenase gene influence provitamin A conversion efficiency in female volunteers. Journal of Nutrition. link
  8. 8Mukherjee S, Date A, Patravale V et al. (2006). Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety. Clinical Interventions in Aging. link
  9. 9Melhus H, Michaëlsson K, Kindmark A et al. (1998). Excessive dietary intake of vitamin A is associated with reduced bone mineral density and increased risk for hip fracture. Annals of Internal Medicine. link
Related in the handbook (7)
Undermines
  • — Stacking liver, a multivitamin, and cod liver oil can push retinol high enough to quietly thin bones — a real risk if you already have osteoporosis.
  • — If you smoke or recently quit, high-dose beta-carotene pills raise lung-cancer risk; this is a real don't.
Related
  • — The classic eye-vitamin formula started with beta-carotene (vitamin A), then swapped it for lutein after it raised lung-cancer risk in smokers.
  • — A weekly slice of liver is a big preformed vitamin A dose, which is why stacking it with supplements can run high.
  • — Most plant vitamin A rides in as carotenoids, and you absorb far more when those vegetables are cooked with a little fat.
  • — Retinoids do their wrinkle-and-texture work on the face; eating vitamin A won't reproduce it.
  • — An adjacent topic in the handbook.
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