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).
Circumstantial evidence allows a trier of fact to infer that a fact exists. In criminal law, the inference is made by the trier of fact in order to support the truth of an assertion (of guilt or absence of guilt). Testimony can be direct evidence or it can be circumstantial.