Get some blood tests, otherwise you're probably gonna waste money and just turn your urine yellow for an hour after you take whatever pills you buy.
Unless someone has medical issues, or lives in a 3rd world country, there is no excuse to be deficient in any vitamin. Fresh food is readily available and very cheap in all developed countries. A lot of stuff people (idiots) buy from supermarkets isn't actually real food, stick to stuff thats close to how nature makes it.
In the US, supplements are essentially unregulated. You never know what you're buying. No one makes improvements by leaps and bounds after 4 months. Most of the supplements and vitamins we take just produce the world's most expensive ****.
Absolutely correct as is what others have said so far. All your needed nutrients and supplements are all found by eating correctly, and by correctly I mean finding out what works best for your body because what may work well for me may not for you, so there is some experimentation that needs to be done, but if you eat well balanced meals with regular exercise you will be fine. The vitamin and herb industry will lead you to believe, with very reasonable arguments, that buying $250 to $500 a month in their "****" will make you live forever and look young and energetic the whole time, this stuff is all nonsense, in fact most of what they sell you can become toxic not to mention the hundreds of dollars and eventually thousands of dollars you **** down the toilet. The most you should ever need to take is a simple cheap generic once a day multivitamin. The health food and nutrient market is nothing more than a new spin on the old tonic water...ie: snake oil.
Most people on a regular "western world" style diet are already overeating, particularly when it comes to protein. Seen over the whole day, you won't need supplements until you're doing 2-3 hard and planned sessions daily. With that said, I believe I've noticed speedier recovery, hence better payoff from the next session, if I have a nutritionally sensible snack during the ideal time span right after a workout. And bars and shakes are easy to carry around. Makes me less hungry at meals too, so I don't think I've increased the total intake by much.
^^ I use to race at a cat 3 level and still never took supplements, so I don't believe a person needs to do that either at that level UNLESS you are aspiring to go further. HOWEVER, if someone is racing professionally and a coach is saying that you need certain supplements then by all means do as the coach tells you, besides you'll get the supplements for free. This post wasn't about someone racing, it was about an average rider, for the average rider there is no need to get supplements and **** them down the drain.
I think after cycling it's important to replenish, especially the glycogen. I use Hammer Recoverite. I tried whey/protein as a supplement this summer, i didn't notice any difference, in either recovery time or performance. I think what the everyone above is saying is true, supplements in general are a waste of money.