The industry is dominated by three categories collectively: Vitamins, Specialty Supplements and Herbs and Botanicals. These three categories make up 68 percent of all sales while the other three, Meal Replacement Supplements, Sports Supplements and Minerals, combine for only 32 percent of all sales in the supplement universe.

Two of these key supplement categories are struggling. Vitamins saw its single biggest sub-category, multivitamins, grow nearly flat in 2014 after media focused on a study calling vitamins "useless." Specialty Supplements saw their worst growth year since we began tracking the category. Fish oil continued to struggle for a second straight year, and three other key growth drivers for the Specialty Supplement category suffered major declines in sales growth for 2014. Only herbs and botanicals, a favored supplement of millennials, managed to continue their strong growth in 2014 by only slipping by one whole percentage point. With that said, 2015 did not start well for this segment, with the New York Attorney General accusing the industry for widespread mislabeling and adulteration.