Can sun prevent cancer? Scientists promote 'safe sun' for healthy vitamin D production Scientists are excited about a vitamin again. Michael Holick of Boston University lies in a tanning bed at the Boston Medical Center. Holick says some sun exposure is beneficial. Steven Senne, Associated Press But unlike fads that sizzled and fizzled, the evidence this time is strong and keeps growing. If it bears out, it will challenge one of medicine's most fundamental beliefs: that people need to coat themselves with sunscreen whenever they're in the sun. Doing that may actually contribute to far more cancer deaths than it prevents, some researchers think. The vitamin is D, nicknamed the "sunshine vitamin" because the skin makes it from ultraviolet rays. Because sunscreen blocks vitamin D's production, some scientists are questioning the long-standing advice to always use it. The reason is that vitamin D increasingly seems important for preventing and even treating many types of cancer. In the last three months alone, four separate studies found it helped protect against lymphoma and cancers of the prostate, lung and, ironically, the skin. The strongest evidence is for colon cancer. Many people aren't getting enough vitamin D, and it's hard to get from food and fortified milk; supplements are problematic. So the thinking is this: Even if too much sun leads to skin cancer, which is rarely deadly, too little sun may be worse. No one is suggesting that people fry on a beach, but many scientists believe that "safe sun" â 15 minutes a few times a week without sunscreen â is a healthy thing to do.