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A 2011 study based on the trial found that the risk of prostate cancer was elevated by 17% in the group that took vitamin E supplements, which was statistically significant. [8] [13] A 2014 study based on SELECT data found that selenium supplementation increased the risk of high-grade prostate cancer in men who had a higher baseline selenium ...
While serum low 25-hydroxyvitamin D status has been associated with a higher risk of cancer in observational studies, [101] [102] [103] the general conclusion is that there is insufficient evidence for an effect of vitamin D supplementation on the risk of cancer, [2] [104] [105] although there is some evidence for reduction in cancer mortality.
For dietary retinol, no effects were observed for high dietary intake and breast cancer survival, [108] risk of liver cancer, [109] risk of bladder cancer [110] or risk of colorectal cancer, [111] [112] although the last review did report lower risk for higher β-carotene consumption. [112]
Humans can produce some vitamins from precursors they consume: for example, vitamin A is synthesized from beta carotene; and niacin is synthesized from the amino acid tryptophan. [54] Vitamin C can be synthesized by some species but not by others. Vitamin B 12 is the only vitamin or nutrient not available from plant sources.
An inverse relationship between dietary vitamin E and lung cancer was reported in observational studies, [72] but a large clinical trial in male tobacco smokers reported no impact on lung cancer between treatment and placebo, [73] and a trial which tracked people who chose to consume a vitamin E dietary supplement reported an increased risk of ...
A meta-analysis concluded that supplementation with β-carotene does not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally. [8] [40] High levels of β-carotene may increase the risk of lung cancer in current and former smokers.
Long-term supplementation with relatively large amounts of folic acid is associated with a small reduction in the risk of stroke [12] and an increased risk of prostate cancer. [13] There are concerns that large amounts of supplemental folic acid can hide vitamin B 12 deficiency. [1] Not consuming enough folate can lead to folate deficiency. [1]
Taking vitamin D supplements has no significant effect on cancer risk. [98] Vitamin D 3, however, appears to decrease the risk of death from cancer but concerns with the quality of the data exist. [99] Nevertheless, studies suggest that Vitamin D deficiency is associated with increased risk of development melanoma. [100]