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News Stories in Perspective
Vitamin D and Cancer: What Do Researchers See?
Vitamin D has been getting more attention for its potential role in reducing cancer risk. In fact, it was a major topic of discussion at the American Institute for Cancer Research’s (AICR) recent conference on food, nutrition, physical activity and cancer. While there is not ye a global consensus on its role in protection, the nation’s top cancer researchers have a lot to say about the sunshine vitamin.
For some time, laboratory studies have shown that vitamin D helps maintain control of cell growth. At the AICR conference, evidence was shared that confirms vitamin D can help activate certain proteins that suppress tumor growth and development.
The question of how much D continues to be debated. Some research now suggests that the current recommended intake level (400 International Units (IU) daily for most adults) may not be enough to raise blood levels of the vitamin to levels associated with lower cancer risk.
Further complicating the issue are concerns about how to best evaluate vitamin D status. Simply documenting how much vitamin D someone gets from diet or supplements is inadequate because we also produce our own vitamin D in response to sunlight. Calculating the amount produced following sun exposure is also difficult, as age, skin color and environmental pollution can all affect vitamin production.
Experts tend to agree that the best way to assess someone’s vitamin D status is to measure blood levels. Unfortunately, accurate and reliable methods are not widely available. Furthermore, an optimal blood level for the vitamin is not yet clear. Many researchers seem convinced that levels currently thought of as “normal” may not be high enough to encourage optimal bone health or reduced cancer risk. Shockingly, if the highest proposed blood levels of vitamin D are adopted, 50 to 78 percent of Americans will be classified as having low levels of the vitamin.
Despite the wealth of evidence suggesting a link between vitamin D and cancer protection, not all studies reveal a benefit with increased vitamin D intake. Take, for example, the recently published data from the Women’s Health Initiative that failed to show lower breast cancer risk among women who received 1000 milligrams (mg) calcium plus 400 IUs vitamin D daily. Although the women were followed for seven years, some experts suggest that it is too soon to see an impact, as part of vitamin D’s purported effect occurs early in the cancer process, which can take 20 years to develop. Longer follow-up may tell us more.
The research suggests that vitamin D has great potential as one part of a strategy to lower cancer risk. For some of us, boosting intake to the top of the safety margin – about 1000 to 2000 IU per day – may be needed for lower cancer risk. Many experts urge boosting intake now, but others are calling for more evidence before recommending higher intake levels, especially if any genetic differences could put some people at risk.