Hi, author of the blog post here! Yes thank you for catching this awful typo, it's fixed now! I did write "4000 or 5000 IU of Vitamin D" everywhere else in the article -- main text, conclusion -- just my luck that the one place I mess up is right at the very start.
(Do not take 5000 mg, that's 200,000,000 IU. You'd have to chug dozens of bottles per day)
(Do not take 5000 mg, that's 200,000,000 IU. You'd have to chug dozens of bottles per day)