Summer means long, languid afternoons spent at the pool, in a hammock, or on vacation. People enjoy the opportunity to work reduced hours, check out mentally, and spend hours recapturing their energy in the warm sun. But does all this luxurious laziness have unfortunate consequences?

For kids, it certainly does: The Colorado Department of Education noted that the "summer slide" is real, enabling children to lose some of the learning they achieved over the previous school year -- lower-income children lose an average of two months' worth of reading skills, which has a snowball effect over each summer. Research has shown that summer reading initiatives can staunch the bleeding of skills and keep kids ready for the next school year.

Science has proven that children's brains are structured differently than adult brains are, but this shouldn't necessarily give grown-ups relief: Brain volume peaks in our 20s and declines thereafter. Most notice memory slowdown starting in their 40s, when the brain's cortex -- the center of cognition -- shrinks. That means we likely suffer just as much as kids do when our schedules slow down and our brains take an extended break.

One way to combat that is by starting a summer reading list that feeds the mind beyond breezy "beach reads." Here are 11 to consider: 

A certified financial planner with Wealthquest, Lenhoff has met dozens of older clients who scrimped and saved their entire lives, following the playbook they'd been given -- only to find the "rules" didn't leave them feeling fulfilled. They had lots of money, but no experiences to show for it. In this book, Lenhoff shares the stories of people who have faced financial regret and explains how others can find peace of mind about money without following utilitarian rules. The book explores everything from how to give yourself permission to be generous to how to instill healthy attitudes about money in your children.

Sandberg's "Lean In" received both acclaim and criticism for its call for women to lean into their careers; this book, written after her husband's unexpected death, takes a different tack. She discovered she couldn't simply power through her circumstances; emotion plays a distinct role in people's ability to triumph. She worked with Grant, a psychologist, to unravel the steps people can take to build their resilience. Discussing everything from how to help others in crisis to creating companies that can persevere, the book explains how to make the most of Plan B.

3. "Beyond Barriers" by Nikki Barua

Barua runs an innovation consultancy -- working with Google, Disney, and more -- that has taught her a lot about "leveling up." Barua believes we must break through the barriers preventing us from maximizing our potential. Speaking from her experience as a Millennial woman in the workforce, she discusses the framework she used to find clarity, harness her courage, and sustain her conviction.

This book dives into the crimes committed against the Osage Nation. Living on top of oil, the tribe became incredibly wealthy in the 1920s, celebrating a Gatsby-like existence in the oil fields of Oklahoma. But the tribe's members began to die under mysterious circumstances, and the people who investigated the unusual deaths met with a similar fate. J. Edgar Hoover's FBI took control of the investigation, utilizing an undercover team to help the Osage determine why its members were being murdered.

5. "Your Oxygen Mask First" by Kevin Lawrence

Lawrence applies the standard airline safety tip -- put your own oxygen mask on before helping others -- to the business world. He posits that while it's counterintuitive, the best leaders take care of themselves before pouring their energy into helping others. Developed as a playbook of sorts, Lawrence's work offers practical tools to end old habits and begin new ones.

Landrieu, best known as the New Orleans mayor who took down the city's Confederate statues, explores America's reactions to his decision and analyzes the historical underpinnings of the statues themselves and the feelings they still evoke. Part memoir, part historical analysis, the book discusses the implications of slavery and the systemic racism prevalent in the United States, both during the Civil War and after. As discussions about race continue to take center stage, Landrieu offers an interesting view into how we reconcile our present with our past.

Medicine, once a regaled industry, is now reviled by some who feel the field has become more focused on making money than treating patients. Rosenthal's book studies the American healthcare system, exploring how profits have been championed by politicians, administrators, insurance companies, and pharmaceutical corporations to patients' detriment. While examining the shift from care to revenue, she explains how the system could change still to remove what ails it.

"Windtalkers" made Native American code breakers famous; this book examines the women who made an impact as code breakers during the second World War. These female cryptographers -- numbering more than 10,000 -- helped the U.S. military break codes from Washington, D.C. From intercepting crucial messages to determining the underlying meaning of a message, these women built scientific- and communication-based careers. While their efforts were hidden, Mundy located surviving code girls to paint a complete picture of their work.

Hong's book examines the winding path to success -- not overnight success stories. It offers a unique outlook on how people can take the road less traveled to overcome obstacles and expectations society has placed on them, both personally and professionally. Addressing everything from reframing weaknesses to building a vertical network to trading social value, Hong offers unconventional career-building methods to those stuck in a rut.

Evans, an ultramarathoner, used the sport to overcome mental health struggles and raise money for charity; his belief that the human body and mind are capable of more than we can fathom led him to run a race down Mt. Everest. He shifts the lessons from his endurance career and his struggle with anxiety and depression to help others learn how to manage turmoil and stress, explaining the "how" of gaining mental toughness.

As border control and immigration remain hotly debated topics, Cantú's book arrives to shed a new perspective on the situation facing the United States and Mexico. Cantú grew up in the Southwest and joined the Border Patrol as an adult. After years of tracking drug routes and smuggling corridors, he left the Patrol to escape the burden of what he'd seen. He was dragged back into the world of the frontera when a friend visiting his mother in Mexico didn't return, pushing him to find out what happens after the Border Patrol gets involved.

While summer is a time of relaxation, it should still include some mental stimulation. These 11 books can be the foundation of a summer reading list that makes you think and see the world through a new lens.