As much as I preach “food first”, supplements can be necessary in maximizing our diet to complement our training. It is often much more practical to bring a scoop of protein powder with you to your workout than it is to bring rice and beans. It is a reasonable concern to questions ones vitamin D status if they train indoors year round, limiting sun exposure. Depending on where you live, you may have access to different foods than others. Supplements are created just for that, to supplement our diet when it is lacking.
The best thing we can do in these situations is ask ourselves two things first. One - am I doing everything I can to get the nutrients I need through food? And two - should I have my *nutrient of concern* levels checked by my primary care provider?
If your sports RD or primary care provider has clinically identified a nutrient deficiency and recommended a supplement, then certainly listen to that recommendation. If you heard about a supplement or one of your teammates recommended one, please check with your sports RD first before consuming it.
The dietary supplement industry is not regulated by the FDA. Which means that we don’t know what is in the bottle, or how much, or if anything extra has been added to it. I am always sad to read that athletes are failing drug tests and banded from their sport for a substance that was unknowingly in a supplement they were taking. This can be prevented if we only consume supplements that are third-party tested. This means that an outside lab tests and confirms that what is on the label is in the bottle. NSF Certified For Sport and Informed Choice are two of the more common labs and you can search their website to find safe supplements to support your training demands.
https://www.teamusa.org/nutrition < Click the ‘Supplements' Factsheet
https://www.examine.com < Great resource to learn more about the latest research behind supplements