In a new study, researchers found that breast-cancer patients who had high levels of vitamin D were twice as likely to survive [as] women with low levels. They reviewed five studies that observed more than 4,440 women. "The study has implications for including vitamin D as an adjuvant to conventional breast cancer therapy," study co-author Dr. Heather Hofflich, an associate professor of medicine at the University of California San Diego, said in a press release. The researchers recommend that vitamin D should be added to the various treatments given to women fighting breast cancer. The body naturally produces vitamin D when exposed to sunlight, but milk, fatty fish and other foods can also boost production. Patients could also take vitamin D supplements.