The VITAL trial, which focused on cancer and cardiovascular health, recently published two results papers: one paper comparing those assigned to vitamin D (2000 IU/day) vs. placebo and another paper comparing those assigned to omega-3s (1000 mg/day) vs. placebo. You may have read in the news that this study showed that neither vitamin D nor omega-3s prevent cancer (all kinds of cancer analyzed together) or heart disease (a composite of all types).
However, when the separate types of heart disease or death from cancer were analyzed, there were 30 different very significant results.