Word of advice: don't take vitamins ADEK without advice from a physician for extended periods or in high doses. These are fat soluble so you can have too much of them.
I know it sounds downright crazy, but it's possible that someone who's studied medicine and practiced it for years, actually knows better than random anonymous forum users.
As the link in the OP actually denotes, no, that's not always the case.
Bodybuilders and performance trainers - as well as Soviet Union sports scientists - have known for decades that Vitamin D supplementation is vital. This has been rejected by a significant number of general practitioners and other medical experts who are and were anti-supplement simply out of rote thinking.
Yes, people should be tested for their levels. But this simply isn't feasible for poor people, and telling them to get serum tests for Vitamin D before taking a lower-bound amount of the cheap supplement from the grocery store is ridiculous.
http://www.rollingstone.com/sports/news/russia-banned-from-2...
It is always possible to arrive at a correct conclusion through entirely incorrect reasoning.
Or, as the saying goes, a broken clock is right twice a day.
Homeopathy is crap. But bodybuilding/powerlifting/athletic training often finds the answers well ahead of peer-reviewed science.
A fruit or vegetable that have traveled thousand of miles before being delivered to you has almost no vitamins left in it and probably didn't have much to start with considering soil depletion.
I believe (emphasis on believe) that supplementation is necessary even if you "eat right".
Truth be told, doctors still don't know much about IBS and/or Crohn's. Or even conditions like rosacea and/or dermatitis. Mark my words, better gut flora/microbiome will be the cure for these conditions in the near future and doctors will contest this up until the evidence is too loud to ignore.
For instance, overdose quantities may be different among the various vitamers of a specific vitamin. Your physician will advise you not to supplement ADEK because people have overdosed on retinol or ergocalciferol, whereas you can eat carotene until you literally turn orange, and 15-30 minutes of daily midday sunlight can make 10000 to 20000 IU each time.
The danger of vitamin D oversupply (even as cholecalciferol) is calcium related, which is why you have to balance it with vitamin K (as menatetrenone), but it's called vitamin K from the German for "clotting factor", so then your doctor worries about clots. But vitamin E (as RRR-alpha-tocopherol) is also an anticoagulant. It's almost as if you have to consider every vitamin as just one part of a balanced system of nutrition...
So in order to give you good advice, your doctor would have to have detailed and intimate knowledge of your current nutritional state and your physiology, but we only have 15 minutes and I don't want a malpractice suit for giving you the wrong advice, so just f' it and give 'em the boilerplate: "You don't need to supplement. Just eat a balanced diet with plenty of dark green vegetables, and get some exercise."
So there you go. I just saved you a copay, unless your particular physician has an interest in nutrition-based medicine.
Don't get your vitamins from the corner pharmacy or the grocery store. Most of them will use the cheapest chemical that technically qualifies as a particular vitamin. You need specific vitamers if you intend to exceed the general recommendations. Do your own research, and remember that you can damage your own body by doing something stupid with it. If you consult a physician, make sure they have enough training and education to be credible with respect to nutrition and biochemistry before you fork over money for an office visit. You can read the same articles and papers that they read, if you are motivated enough to do so.