High intakes of preformed vitamin A can cause serious side effects — symptoms include severe headache, blurred vision, nausea, dizziness, muscle aches, and problems with coordination.[1][2][3][4][5]
Excessive intakes of preformed vitamin A have been associated with an increased risk of bone problems — e.g., osteoporosis and hip fracture[6][7] — and some types of cancer, including ovarian cancer,[8] pancreatic cancer,[9] lung cancer,[10] and gastric cancer.[11] However, this evidence is derived from observational studies using cross-sectional and cohort study designs in which vitamin A intake data was estimated from historical diet recall using food frequency questionnaires. This makes it difficult to prove the causality between vitamin A intake and disease risk.
Excessive intake of preformed vitamin A during pregnancy can also cause birth defects, and excessive intake when breastfeeding can impair a child’s growth.[1][2][3][4] Therefore, high-dose supplementation with preformed vitamin A is not recommended when pregnant or lactating — consult your doctor if you are unsure.
In severe cases, excessive intake of preformed vitamin A can cause coma and death,[1][2][3][4][5] and supplementation with high doses of vitamin A has also been associated with increased mortality in well-nourished populations.[2]
There are also several drug interactions with Vitamin A, including, but not limited to, several antibiotics, some weight loss drugs (e.g., orlistat), and vitamin-A-containing drugs (e.g., isotretinoin). Always consult your doctor if you are taking over-the-counter or prescription medicines and planning to use a vitamin A supplement.
Because of the side effects and potential toxicity, there is an upper limit for total daily intake of preformed vitamin A (from food, beverages, and supplements combined):[1][12]
| Ages | Upper limit of daily intake |
|---|---|
| Birth to 12 months | 600 micrograms (mcg or µg) |
| Children 1–3 years | 600 mcg |
| Children 4–8 years | 900 mcg |
| Children 9–13 years | 1,700 mcg |
| Teens 14–18 years | 2,800 mcg |
| Adults 19 years and older | 3,000 mcg |
Unlike preformed vitamin A, high intake of beta-carotene (a provitamin A carotenoid) is not associated with serious side effects or health problems, and beta-carotene does not have an upper limit of intake. However, this does not mean that taking a higher-than-recommended dose of beta-carotene induces a greater effect.