A deficiency of riboflavin can be primary - poor vitamin sources in one's daily diet - or secondary, which may be a result of conditions that affect absorption in the intestine, the body not being able to use the vitamin, or an increase in the excretion of the vitamin from the body.
Substantial evidence means more than a mere scintilla. It means such relevant evidence as a reasonable mind might accept as adequate to support a conclusion.. Richardson v. Perales, 402 U.S. 389, 401 (1971).
As far as I know, substantive refers to something being real. If evidence is substantive, it means that it is real, convicing, and powerful. Substantial evidence, on the other hand, refers to the amount of evidence. Substantial evidence would in other words mean there is a lot of evidence.