The world of nutritional supplements can be a minefield for athletes.

''If you just go to your strength coach and get supplements, you're fine,'' said Darren O'Day, a reliever for the Baltimore Orioles this past season. ''If you walk into a GNC, you're playing with fire.''

With that in mind, a line of supplements called Klean Athlete announced an agreement during the All-Star break with the Major League Baseball Players Association. The benefit to Klean was obvious - the union was giving its seal of approval to the products - but the MLBPA hopes this deal will also help its members. It's one of several ways the union has tried to make it easier for baseball players to find supplements without having to worry about violating the sport's drug agreement.

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Now Klean is reaching out to another sport. With the Olympics less than a year away, Klean Athlete is set to announce Monday a new partnership with USA Water Polo. Klean will provide supplements and nutrition education to U.S. national teams in that sport.

''We have a lot of young girls on the team, and It's kind of a learning process when you go through training for the Olympics,'' said Courtney Mathewson, a member of the gold medal-winning U.S. team from 2012. ''It's definitely hard on your body and your mind, and to be able to know that you're putting everything in your body that is NSF safe and good for your body . I think it's reassuring to us.''

The NSF Certified for Sport program approves products through a rigorous testing process, validating them for athletes who need assurances that what they're taking is allowable under whatever drug policy they need to obey.

''There are almost 500 companies in our auditing program. There are over 400 products in the NSF Certified for Sport program,'' NSF International technical manager Lisa Thomas said. ''So there's plenty to choose from. It's just, the dietary supplement industry, it's a $37 billion industry in the U.S. alone.''

So there are lots of products out there that aren't certified, and that's cause for concern.

The MLBPA's deal with Klean Athlete is not exclusive, but the union clearly feels confident promoting this line of supplements. Klean has partnered with NSF International and can provide certified products.

''They are in many ways the gold standard here,'' said Tim Slavin, director of business affairs and licensing for the MLBPA. ''Their business model tracks what we want. This is about being healthy, access to nutritional supplements that are safe - certainly NSF certification is a threshold bar. Without it, nothing happens.''

The question now is how many players will use the Klean products - and more broadly, whether the work the union has done will reduce the number of drug suspensions that can be attributed to nutritional supplements.

Baseball's joint drug agreement spells out a protocol in which teams are required to provide nutritional supplements to players. Those supplements must be validated by the NSF program.

Ryan Stoneberg, strength and conditioning coordinator for the Kansas City Royals, says Klean Athlete offers specific nutrients separately - which isn't necessarily ideal. Some players may prefer products that combine nutrients.

''If you want to be very specific about what you want to take, (Klean Athlete) can provide it in, like, medical grade, which is very good,'' Stoneberg said. ''Problem is, you don't see a lot of individuals in this environment saying, `I want this one specific nutrient.' They don't want to take 10 different pills.''

The union's deal with Klean was announced without much fanfare, and there's plenty of work to be done to raise awareness within baseball. Klean Athlete says it's exploring opportunities to offer educational sessions to players during spring training next year.

Representatives from Klean have already met with water polo players to talk about the benefits of their products. Mathewson said she didn't sense any pressure to use Klean's products, but it never hurts to have a number of options.

''Every athlete is different on this team. There's different ages, sizes, shapes, everything,'' she said. ''These are just kind of some supplements and resources that are available to us. ... It's just nice to be able to have those resources there if you need them.''