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There has been some research looking into whether blood levels of certain vitamins are good indicators of someone's cancer risk but don't get too invested just yet. "That is one of the messier areas of study," says Colditz. It's particularly messy when it comes to vitamin D. Some studies have shown that low levels of vitamin D are associated with an increased risk of breast and colon cancers but other studies have shown that high levels can also indicate elevated risk of certain cancers. A 2013 study found that high B12 levels may be a marker for several kinds of cancer but, again, the research is just beginning.