You already know that vitamin D is good for your bones, your brain, and your heart. Now, new research suggests that it may also give your workout routine a boost. According to a study published in the European Journal of Preventive Cardiology, people with higher levels of vitamin D tend to be more physically fit.

Specifically, the study looked at cardiorespiratory fitness, a measure of how efficiently the heart and lungs supply oxygen to the muscles during exercise. People with higher cardiorespiratory fitness can exercise longer and harder, and they also tend to live longer and healthier lives.

For the study, researchers compared the vitamin D levels and cardiorespiratory fitness levels—measured by a treadmill test—of nearly 2,000 U.S. adults ages 20 to 49 who took part in a nationwide study from 2001 to 2004.

They found that people in the top quartile of vitamin D had cardiorespiratory fitness levels that were 4.3 times higher than those in the bottom quartile. Each 10-point increase in vitamin D was associated with a 0.78-point increase in VO2 max, the measurement for cardiorespiratory fitness.

RELATED: 12 Ways to Get Your Daily Vitamin D

Even after adjusting for participants’ age, sex, race, body mass index, and health history, fitness levels for those with the highest vitamin D levels were still 2.9 times higher than those with the lowest. The link held true for both men and women, and for all of the age groups and ethnicities in the study. It was also true regardless of whether participants were smokers or had hypertension or diabetes.

The study was observational, so it could not show a cause-and-effect relationship. But the association was “strong, incremental, and consistent across groups,” said lead author Amr Marawan, MD, assistant professor of internal medicine at Virginia Commonwealth University, in a news release from the European Society of Cardiology (ESC).

“This suggests that there is a robust connection and provides further impetus for having adequate vitamin D levels,” Dr. Marawan said, “which is particularly challenging in cold, cloudy places where people are less exposed to the sun.”

Vitamin D is known as the sunshine vitamin because the human body makes vitamin D in response to sun exposure. People can also get it from supplements or from fortified foods. (The study did not take into account how much vitamin D participants got from sun, supplements, or food.)

The study notes that vitamin D could potentially affect cardiorespiratory fitness in several ways. For starters, the nutrient has been shown to boost the production of muscle protein and aid in calcium and phosphorus transport on a cellular level. It may also affect the body’s makeup of fast-twitch muscle fibers, “suggesting that vitamin D may improve aerobic fitness,” the authors wrote.

RELATED: 27 Health Problems Linked to Low Vitamin D

This isn’t the first study to suggest a link between vitamin D and athletic performance: Previous research has noted that vitamin D-deficient ballet dancers jump higher and have fewer injuries—and pro athletes have better sprint times—when they take supplements…

What would you do if you were out for a Saturday morning run, training hard for your next race, and all of a sudden a car drives by and throws a McDonald’s cup at you? What about if a group of young boys comes up behind you and smacks your butt, giggling as they run away?

Believe it or not, both of these examples of supreme body shaming have happened to competitive runner Julie Creffield, author of The Fat Girls' Guide to Marathon Running ($9; amazon.com)

Creffield, who’s from the United Kingdom, considers herself a plus-size runner. But anyone who thinks her weight holds her back is seriously mistaken. She’s been running for about 15 years and has completed marathons, ultramarathons, and triathlons around the world. Now, she’s taking on what she calls her “bucket list” race: Sunday’s New York City Marathon.

RELATED: Everything You Need to Know to Train for a Half Marathon

For Creffield, 15 years of running has also meant 15 years of body shaming, exclusion, and misguided stereotypes. “People automatically think you run to lose weight, and then when you don’t lose weight, they’re like ‘Why are you still fat?’” she tells Health. “There’s this assumption that we only exercise for slimness, and for me that’s not the reason.”

Running is like therapy for Creffield. She used to struggle with depression, she says, and she credits exercise with pulling her out of it.

Another misconception Creffield can’t seem to escape: people thinking she’s a beginner. “They give you unsolicited advice about how to improve, and they say things like, ‘Once you’ve been doing it for a while, it’ll be easier.’ And I’m like, ‘Well, I’ve been running for 15 years.’”

RELATED: 6 Food Rules for Marathon Success

After years of putting up with body-shaming comments and actions, Creffield says she realized she couldn't be the only runner who had to deal with this kind of abuse. So in 2010, she started her blog, The Fat Girls' Guide to Running. In 2013, she turned it into a business, Too Fat to Run?

The name was inspired by one of Creffield’s most notable body-shaming experiences, when she went to the doctor with a pulled back muscle. As soon as she started complaining of pain, the doctor suggested she exercise more. “I was like, ‘Well actually, I’m training for a marathon,’ and he said, ‘Oh no, you’re too fat to run a marathon.’” Cue her determination to prove him wrong.

She calls her business a “virtual running club,” or an online resource runners can go to find carefully tailored workouts and training programs. It's also a platform for connecting with other women in the program. 

Creffield says she’s always felt excluded from the running community…

Hotly debated fitness topics are in no short supply: yoga vs. pilates, cardio vs. strength training, and the treadmill vs. outdoor running. But no dispute is as polarizing as the one surrounding morning vs. evening workouts.

Of course, the absolute best time to work out is whenever gym time meshes with your schedule so actually show up on the regular. If you can only squeeze in a jog or yoga flow late at night, it's smarter to do that then skip it altogether, exercise physiologists and trainers say.

But starting the day with a heart-pumping sweat session does come with indisputable health benefits. And now that daylight saving time has ended, mornings are brighter, so getting out of bed and into your workout leggings isn't as hard as you might think. Let us make the case with these five science-backed reasons to start setting your alarm a little bit earlier.

RELATED: How to Motivate Yourself to Go to the Gym on Cold, Dark Days

You’ll make better wellness choices all day

“When you start the day working on your health, you'll strive to maintain that healthiness," explains Zack Daley, head coach at Tone House in New York City.

Think about it: When you're proud of yourself for killing it at your 8 a.m. class, you won't want to ruin that healthy high by gorging on breakfast donuts, right? Instead, you'll likely try to keep that awesome feeling going by skipping the pastries, taking the stairs to get to your office, and indulging in a grain bowl at lunch rather than the taco Tuesday special. All of these little moves add up to a healthier you.

You’ll sleep like Sleeping Beauty

According to the  National Sleep Foundation (NSF), people who hit the treadmill at 7 a.m. sleep longer, experience deeper sleep cycles, and spend 75% more time in the most reparative stages of slumber than those who exercise at later times in the day. THe NSF also notes that those who sweat at night tend to have more trouble catching shuteye, possibly because working out raises your body temperature, which is a known sleep saboteur.

Anecdotally, Daley believes this to be true: “I find that when I work out early, I am able to get to bed easier at night. But when I work out later at night, my adrenaline is still going from my late night workout.”

RELATED: 20 Habits That Make You Miserable Every Winter

You might lower your blood pressure 

People with high blood pressure, aka hypertension, often need medications to control this dangerous condition. But lifestyle changes—such as morning exercise—may help. In one study published in the Journal of Vascular Health and Risk Management, researchers had participants exercise at three different times of day: 7 a.m., 11 a.m., and 7 p.m.

Those who worked out early in the morning reduced their post-workout blood pressure by 10%…