While this is a very interesting paper, I'm a little bit wary of research articles that only have a single author. Are you aware of how accepted this viewpoint

While this is a very interesting paper, I'm a little bit wary of research articles that only have a single author. Are you aware of how accepted this viewpoint is in the wider research/medical community? For example, are there any medical bodies that currently actually recommend adults to take 8000 IU of vitamin D supplement per day, if they are at risk of deficiency? Conversely, are the medical bodies that do not make such a recommendation simply slow, or are they in fact disputing the above findings?