Jennifer Aniston has signed on as Chief Creative Officer of a company that makes a range of so-called “collagen” products to promote healthy hair, nails, skin and joints.

“I’ve always been an advocate for nourishing your wellness from within, which is why I started using Vital Proteins so many years ago,” said Aniston in a statement.

But no scientific evidence exists that suggest they work as advertised.

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In the fine print, they include a standard disclaimer: “These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.”

So then, what good are they?

In our health obsessed society it doesn’t take much to convince someone that a miracle product will bring about all kinds of positive results.

But when you add endorsements from glamorous celebrities, the credibility of the product gains new traction–and attention.

Collagen products are the latest fad health trend.

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This year alone, consumers are expected to spend $293 million on Collagen Supplements, up from just $50 million in 2014, according to market research firm Nutrition Business Journal.

The market is projected to reach $6.5 billion by 2025 as collagen makes its way into more foods and beverages, topicals, and even the operating room.

Dr. Mark Moyad, director of the complementary and alternative medicine program at the University of Michigan Medical Center calls the trend the “most wacky and controversial.”

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“It’s definitely among the top three products people ask me about, and I believe it does hold promise in some diverse areas of medicine,” he told WebMD.

Collagen definitely plays an important role in the body.

It makes up about 75 percent of your skin, keeping the skin supple and smooth.

It also contains amino acids that are used to maintain and repair your tendons, bones and joints.

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Anniston’s commercial benefactor, Vital Proteins, notes that natural collagen production begins to decline as we age.

As people age collagen breaks down faster than it can be replaced. The loss of about 1 percent of collagen per year begins in our mid-20s.

Women can lose as much as 30 percent during the first 5 years of menopause.

The loss of collagen caused the skin to dry out, causes wrinkles and leads to crepe skin in older adults.

Sun exposure, cigarette smoking and air pollution can also accelerate collagen breakdown, according to medical references.

But that’s where science ends and unsubstantiated claims begin.

It seems logical that simply replacing collagen would be beneficial, but the science is more complicated than that.

Powders, topical creams and injectable liquids are all on the market, and each have drawbacks.

Topical creams are not absorbed easily by the skin. Injecting collagen provides only a temporary fix and both can produce allergic reactions.

That has caused a shift in marketing to powders and food supplements. That’s where things get murky.

Natural collagen produced in the body is a form of protein. But simply ingesting collagen in food supplements doesn’t mean it will be absorbed by the body as a protein.

The body also produces an enzyme known as collagenase that routinely breaks down collagen as part of its normal immune response.

The digestive system converts all proteins to amino acids, which are not quite the same. Plus there is no way for products to target the skin, bones or other organs.

Stomach acids break down collagen proteins you eat before they reach the skin intact, Dermatologist Lauren Eckert Ploch told WebMD.

And, its possible to produce a negative reaction by flooding the body with too much amino acid.

A 2012 study published in the American Journal of Clinical Nutrition found that a person can safely consume about 35 grams per day.

This standard was set based on the reactions of healthy adult men, so this limit may be a bit lower for others, the study stated. Most supplements contain about two to three grams per day.

The side effects range from an upset stomach, nausea, headaches, or fatigue to a loss of coordination, low mood and sleep-cycle issues.

Most of the collagen products on the market are actually collagen peptides.

That’s a type of protein made from ground-up fish or chicken, pig, and cow skin and bones.

The problem is “these parts tend to act as sponges for contaminants and heavy metals,” says Ploch.

Ground-up cow hooves, hides, bones and nerve tissues — a chief source of collagen supplements — could also carry diseases like bovine spongiform encephalopathy (BSE), or mad cow disease.

In 2016, the federal Food and Drug Administration (FDA) prohibited the use of some cow parts in dietary supplements to “address the potential risk” of contracting BSE.

Consumerlab.com tested 14 well-known collagen supplements and discovered at least one contained high levels of cadmium, a toxic heavy metal.

Because production of collagen supplements is largely unregulated, quality can vary widely. The FDA only recommends “good practices” to follow in manufacturing.

Nonetheless, collagen supplements have played a role in naturopathic medicine for centuries in China and other cultures.

And, there is a large body of anecdotal evidence and some limited scientific studies that show they could have a beneficial effect on the body.

Some products also include additional supplements.

Vital Proteins most popular product, for example, also includes hyaluronic acid and vitamin C. The company says they help promote natural collagen production and a more youthful appearance

Aniston will star ina new Vital Proteins campaign in December on social media and broadcast.

It will feature a “day-in-the-life look” at how She uses Vital Proteins products.

Vital Proteins was founded in 2013 by Kurt Seidensticker on the belief that whole food-based collagen nutrition is fundamental to maintaining overall health and longevity, according to the company.

While collagen supplements are trendy, Valori Treloar, a Massachusetts dermatologist and nutritionist, says it’s possible to get the same benefits from homemade stock using bones from chicken, fish or beef.

“I think collagen is interesting and there is some data out there suggesting benefit, but I prefer for my patients to eat food,” she says.