If you’ve read a health and beauty magazine at any point in the past few years, you’ve come across mention of the collagen craze at least once. Depending on who you hear it from it can either sound like an elixir from the fountain of youth or just another mystery supplement and fad. But while the hype over collagen feels recent, not many people know what it is, how it’s taken to help people, and what it even does. It comes in powders, in pill form, and plenty of other forms. It’s said to help digestion, joint health, it can help you sleep, lose weight, and even improve the elasticity of your skin as you age — again, just to name a few things.

So exactly is this collagen craze all about?

Collagen is actually the most abundant protein in the body, giving structure to our skin, our bones, and our muscles. It’s a natural building block of many parts of the human body, with at least 28 different types of protein and three, in particular, making up as much as 90% of the proteins in your body.

In your skin, collagen makes up the middle layer, known as the dermis. Production of it starts to naturally slow down as we age. “After the age of 25, we break down more collagen than we make so that’s why we start to see fine lines and wrinkles,” says Debra Jaliman, MD. “Under a microscope, you see fragmentation of the collagen network in the dermis — this is the hallmark of skin aging.”

Here, boosting collagen peptides in your diet with supplements improves skin elasticity and slows the signs of aging on the skin. 

In your joints, collagen peptides make you more resilient to injury. A 2008 study found athletes who took hydrolyzed collagen for six months saw an improvement in joint pain. Other studies show that it assists with back and knee pain as well, and it also increases the amount of calcium in your bones and helps form new bones. Again, we see how it’s a natural building block whose absence as we age aligns with troubles we start to encounter more often.

Glycine is an amino acid in collagen that calms the nervous system, coming into play when we sleep. One study discovered that people with sleep troubles fell asleep quicker, had deeper sleep, and experienced less daytime drowsiness the following day when they’d taken glycine before bed. Meanwhile, when we’re awake, glycine converts glucose into energy and helps us develop muscle, which in turn boosts our metabolism and helps us burn fat. Therefore, collagen is also a necessary supplement for weight loss.

And finally, collagen repairs the stomach lining in your intestines, making it easier to absorb nutrients. A “leaky gut” is the result of holes in the intestine allowing toxins, food particles, and bacteria to pass through. Glycine helps with all of these, rounding out the long list of benefits people have found by taking collagen supplements.

And that, more or less, is why there’s such a craze over collagen.