This article originally appeared on Time.com.
The word “collagen” comes from the Greek word for glue, and that’s a helpful way to think about the role collagen plays in your physical health. In your skeleton, tendons, muscles, skin and even your teeth, collagen is a structural protein that binds cells and tissues together while helping them maintain shape and integrity.
But your body produces less and less collagen as you age. And some supplement- and food-makers are marketing collagen products as a way to boost your body’s levels of it.
“Collagen is basically the sale of amino acids,” says Dr. Mark Moyad, director of preventative and alternative medicine at the University of Michigan, and author of The Supplement Handbook. Amino acids are protein’s building blocks, and supplements and foods that have collagen contain chains of collagen-derived protein amino acids—or sometimes just the amino acids themselves, separated from their bonds, Moyad says. There are different types of collagen; some are derived from animal bones or skin, and others from animal cartilage.
It makes sense that consuming extra animal-sourced collagen—whether as a supplement powder or in a food like bone broth—could help the body replenish its stores of diminished collagen. And some research supports this idea. “There are many preliminary trials showing potential benefits for everything from osteoarthritis to skin improvement,” Moyad says.
One 2008 study from Penn State University found that athletes who, for six months, took a hydrolyzed collagen supplement—basically collagen proteins that have been broken down into easily digestible amino acids—experienced less joint pain during activity and at rest. Similar studies have linked collagen supplements to lower rates of back pain or reduced knee pain among people with osteoarthritis.
Meanwhile, research has also linked collagen supplements to improved skin elasticity and skin moisture.
But Moyad emphasizes that all of this research is preliminary. “The studies are weak in general,” he says—meaning small in scope, short in duration or not yet replicated by follow-up experiments.
Also, it’s not at all clear that eating collagen increases your body’s levels of it. As nutrition researchers have shown over and over again when it comes to dietary fat, just because a food contains something doesn’t mean your body will absorb or produce more of it.
Moyad says he also worries about contaminants in collagen supplements and foods. “Since this stuff comes primarily from ground-up animal parts, I would want to know the heavy metal content of these supplements, and also the creatinine content,” he says. Harmful heavy metals like copper and arsenic have turned up in meat products, and creatinine is a toxic breakdown product that comes from muscle tissue.
“I do not want heavy metals or creatinine in my body,” Moyad says. He adds that he’s also seen collagen supplements linked to side effects like nausea, diarrhea and other gastrointestinal issues.
It isn’t yet clear how much collagen, or exactly which type, is most effective. Moyad says that cheap grocery store gelatin—which is derived from animal collagen—may be just as good for your joints and skin as pricey supplement powders. “But no one’s done the studies, so we don’t know,” he says.
He says he doesn’t see any major risks in someone trying a collagen supplement for a couple months to see whether it works for them. But stop if you experience any side effects or have any GI issues.
If you’re going to give collagen a go, Moyad says he’d also want you to consider the lifestyle choices that damage collagen as you age. These include smoking, high blood sugar, sun exposure, a sedentary lifestyle and weight gain.
“If you are taking these [collagen] supplements but not making lifestyle changes, that’s kind of like putting premium gas in your car but not changing the engine oil or doing anything else to maintain it,” he says.