If they are not grouping people by genetic risk than any of these nutritional interventions will always show a low impact.

Of course vitamin D is going to help some people more than others based on their genetic heritage. I am one of these people, and I get most of my vitamin D needs from my diet, mainly fish. Sun exposure might not be the best route for people to get their vitamin D, and this is especially true for light skinned northern people.

I ignore these genetically diverse nutritional studies and just focus on the metabolic pathways and my own genetics.