Consuming fish oil on a regular basis may help increase a person's immunity to sunlight according to a study completed at the University of Manchester and published in The American Journal of Clinical Nutrition.
Fish oil, or omega 3, is an essential fatty acid. Our bodies do not produce them but they are considered necessary for good health. Omega 3 fatty acids help reduce inflammation and have been most commonly associated with heart health but studies have also found associations between them and many other diseases and health conditions. Cognitive and behavioral function may also be linked to omega 3.
According to the University of Maryland Medical Center, omega 3 fatty acids may help:
Some studies have also shown omega 3 to help in the prevention of skin cancer. A study on mice completed at the Baylor College of Medicine in Houston, TX. In 2006 showed a reduced number of tumors as well as a slower progression of skin cancer in mice that were given high levels of omega 3 fatty acids. 
The recent study involved 79 healthy human participants; it was the first study of its kind that involved people rather than mice. Participants were given daily doses of fish oil, equal to about 1
½ portions of oily fish, daily. A second group was given a placebo.
Both groups were exposed to sunlight, using either a sunlamp or direct sunlight.
In the group who took the omega 3, immunosuppression was found to be significantly reduced. When the immune system is compromised, such as from chemotherapy, or isn't working properly, the chance of developing skin cancer increases immensely. This is especially true for squamous cell and basal cell carcinomas but there is an increased risk of melanoma as well. Decreased immunosuppression seems to help your body fight the effects of sunlight on the skin.
But, researchers point out, that taking omega 3 does not replace using sunscreen. While omega 3 may be an important step in protecting your skin, and your health, it should be used as a supplemental protection, not the only protection.
Other studies have shown that diet can impact your fight against skin cancer. A study published in 2010 showed that those who follow the Mediterranean diet, high in antioxidants and omega-3 fatty acids had a lower rate of skin cancer, even when they lived in areas where much time was spent outdoors, in the direct sunlight.
"Immunosuppression and Skin Cancer," Date Unknown, Staff Writer, Skin Cancer Foundation
"Omega-3 Fatty Acids," 2011, Staff Writer, University of Maryland Medical Center
 "The Potential of Omega-3 Fatty Acids in the Prevention of Non-melanoma Skin Cancer," 2006, H.S. Black, L.E. Rhodes, Cancer Detection and Prevention Journal