The problem with the "do supplements work" debate is the lack of proper controls. People who imagine supplementation will give them "extra" benefits are clearly going to be disappointed. But the real value of supplements is to make good deficiencies in the average diet. Given the success of junk food, most people subsist on a highly inferior diet that is lacking in most essential micronutrients. Obviously supplements are nowhere near as good as eating an adequate diet, but most people are too busy cramming McSlop and supermarket junk down their gullets to ever come anywhere near an adequate diet. Thus the real comparison is between people eating junk without supplementation versus people eating junk with supplementation. And we know from the few studies that have actually looked at this issue that supplements go some way toward mitigating the deleterious consequences of the appalling modern diet.

Expecting protective effects is absurd. Hoping for some level of mitigation is perhaps realistic. This is all supplements can ever be expected to achieve.