Millennials are pouring money into gym memberships and boutique fitness classes. A financial expert says spending on fitness is a good money decision for 2 key reasons.

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Spending money on exercise can make you happier.

• Millennials are buying pricey gym memberships, but the payoff can be worth the cost.
• According to financial expert Jean Chatzky, spending money on exercise can boost happiness in two ways: reducing stress and making you feel healthier.
• Millennials, who have been called " the wellness generation," don't stop investing in their health at the gym - they also pay more for wellness experiences and quality food.
• Visit BusinessInsider.com for more stories.

Pricey gym memberships have become a status symbol among rich millennials - but the benefits of exercise might be worth the money.

Spending money on experiences typically leads to a longer-lasting, more substantial payoff - and that's partly because such experiences sometimes involve physical activity, according to Jean Chatzky, financial editor of NBC's "Today" Show and author of 11 books.

Spending money on exercise can boost happiness in two ways, one of which is reducing stress, Chatzky said in her latest book, "Women with Money."

"In the short term, exercise makes you feel better because you blow off some steam," she wrote. "In the long term, it makes you physically stronger and more able to handle whatever stresses life is throwing your way."

The research backs her up. People typically experience four stressful life events a year, whether good or bad - but exercise is the one remedy that helps lessen stress in all of them, she said, referring to results from a Fidelity and Stanford University Center For Longevity.

And researchers at Yale and Oxford who recently collected data about the physical behavior and mental mood of more than 1.2 million Americans found that exercise is more important to your mental health than economic status.

Even if you're not experiencing stress, Chatzky said, getting healthier can make you happier.

A 30-year-old communications specialist told Chatzky that her $250-per-month CrossFit class gave her confidence and made her feel healthier, which in turn made her happier.

Read more: Millennials would rather spend money on experiences than on things. There are 4 reasons why that's a smart money move, according to a financial expert

Millennials are the 'wellness generation'

The communications specialist is part of a broader trend of millennials investing in fitness - they've been dubbed the "wellness generation" by Sanford Health, thanks to their increased spending on health and wellness.

Millennials even spend more on fitness than tuition, Jeanette Settembre of MarketWatch reported. A 26-year-old in New York City told Settembre that she spends about $500 a month - or $6,000 a year - on boutique fitness classes.

Some well-off New Yorkers pay up to $900 a month for a membership at Manhattan's Performix House, an elite gym with a rigorous application process, a private entrance, and a content studio for social-media influencers.

Others prefer a $30 SoulCycle spin class or have a $200-plus membership to one of the nation's swankiest gym chains, Equinox, which even offers a $26,000 ultra-exclusive membership for the traveling mogul.

The uptick in spending on wellness fits into the rise of discreet wealth, in which the rich are investing less in material goods and more in lifestyle choices. But gyms and boutique studios aren't the only things millennials are investing in, health-wise.

They also gravitate toward wellness experiences, like the $10,000-per-week Golden Door spa retreat.

"Wellness is increasingly regarded as a modern embodiment of luxury, and accordingly, an array of spas and studios offering treatments like cryofacials, weeklong retreats, and vitamin IV drips are delivering those experiences," Business Insider's Lina Batarags wrote.

That's not to mention their affinity for organic foods in pricey stores like Whole Foods, $10 green juices, and apartments with wellness amenities.