Popeye may have been on to something after all!
Reviewed by Dietitian Jessica Ball, M.S., RD
Key Points
- Vitamin K is a fat-soluble vitamin that exists in two main forms—K1 and K2.
- Best known for blood clotting, researchers have started exploring if it may be associated with respiratory health.
- Vitamin K1—found in leafy greens—was associated with improved lung function.
Whether from a parent, teacher or a healthcare provider, we’ve probably all heard someone tell us to eat our vegetables. And while peas and carrots may come to mind as the classic staples behind this advice, a variety of other veggies have earned their place on our plates, too.
Take kale, for example—the leafy, green nutrition powerhouse has spent years in the spotlight as one of the internet’s favorite health foods. And like other more classic veggies, there’s a reason kale has risen in popularity. For one, it’s rich in various micronutrients, including vitamin K.
Vitamin K doesn’t exactly get the same spotlight as protein or fiber, but emerging research suggests it may play an important role in respiratory health. While it’s a fat-soluble vitamin best known for supporting healthy blood clotting and bone health, researchers have begun exploring whether higher intake of vitamin K-rich foods—such as kale, collards and Swiss chard—may also be associated with better lung function. That’s exactly what a recent study published in The American Journal of Clinical Nutrition set out to explore.
How Was the Study Conducted?
To investigate whether dietary vitamin K was associated with lung function and the risk of developing asthma or chronic obstructive pulmonary disease (COPD), researchers analyzed data from more than 179,000 UK Biobank participants. The UK Biobank is a large, long-term study that follows volunteers over time to learn who gets sick and why so that scientists can create better ways to diagnose, prevent and treat diseases.
It’s important to note that participants included in this analysis did not have impaired lung function—such as asthma or COPD—at the start of the study. These individuals were identified through hospital and primary care records through the Biobank’s available data. Participants were followed for just over 10 years.
To estimate vitamin K intake, participants completed a food survey online. The questionnaire captured intake of just over 200 foods and 30 drinks consumed within the previous 24 hours. The dietary recall was given at baseline or during follow-up assessments.
Because vitamin K exists in two main forms—phylloquinone (vitamin K1) and menaquinones (vitamin K2)—researchers examined both separately. Vitamin K1 is predominantly found in green leafy vegetables like kale, spinach, Brussels sprouts and cabbage. On the other hand, vitamin K2 is mainly found in animal-based foods such as dairy products, eggs and meat.
Over the 10-year follow-up period, researchers linked dietary data with hospital records and primary care records to identify new cases of asthma and COPD over time. They also used measures of lung function to explore whether vitamin K was associated with increased overall respiratory health.
What Did the Study Find?
Researchers found that eating more vitamin K1—the form found primarily in leafy green vegetables like kale, collards, spinach, Brussels sprouts and Swiss chard—was associated with better lung function and a lower risk of developing COPD. In fact, those with the highest vitamin K1 intake had a 16% lower risk of COPD than those with the lowest intake, meaning the likelihood of COPD went from about 23 in 1,000 people to 16 in 1,000 people.
Interestingly, these associations were even stronger among current and former smokers and participants working in occupations with greater exposure to dust, fumes or other airborne pollutants.
On the other hand, vitamin K2—the form found primarily in animal foods like dairy products, eggs and meat—was not associated with COPD and demonstrated weaker and less consistent associations with lung function. Neither vitamin K1 nor K2 demonstrated any association with adult asthma.
So why might vitamin K matter for lung health? Researchers hypothesize that it may be related to a protein called matrix Gla protein (MGP), which helps prevent calcium from building up in soft tissues like the lungs. Vitamin K is a cofactor for MGP—in other words, vitamin K is required to activate MGP—so the protective protein needs vitamin K to function properly. Over time, a lack of vitamin K may contribute to calcification and damage to the lungs’ elastic fibers—changes that are commonly seen in COPD.
While this mechanism applies to vitamin K in general, only vitamin K1 was associated with better lung health in this analysis. Researchers noted that foods rich in vitamin K1, such as leafy greens, also contain many other beneficial compounds that could contribute to lung health, which could help explain these findings. However, more research is needed to understand why the two forms of vitamin K were associated with different results.
Overall, the findings suggest that eating more vitamin K1-rich foods may help support healthy lung function and could be associated with a lower risk of COPD. However, it’s important to note that this study was observational and many other lifestyle factors were not accounted for, so the research cannot prove that vitamin K directly prevents COPD.
How Does This Apply to Real Life?
Researchers concluded that increasing your intake of green leafy vegetables—kale, for example—by one serving a day could help boost vitamin K1 intake as part of a balanced diet. This increase in intake may be associated with better lung function and a lower risk for COPD.
And while this recommendation may feel like another case of someone telling you to simply “eat your vegetables,” it’s possible to make these foods a delicious part of your routine. If you’re looking for a few simple ways to include more vitamin K1-rich foods in your routine, here are a few ideas:
- Stir them into soups or stews. Leafy greens like kale and spinach cook down quite a lot, making them an easy addition to soups, stews and chilis without changing the flavor.
- Blend them into smoothies. Pair leafy greens with naturally sweet fruit, savory nut butter and tart Greek yogurt for a smoothie where the greens are barely noticeable.
- Build a salad. If plain kale or spinach isn’t your favorite, add ingredients like fruit, nuts, cheese or a flavorful dressing to make salads more satisfying.
- Add them to cooked dishes. Stir chopped spinach or kale into pasta, scrambled eggs or stir-fries.
- Branch out beyond kale. Many other leafy greens like Swiss chard, broccoli, Brussels sprouts, collard greens and cabbage are all excellent sources of vitamin K1 and can help increase your intake.
And if you need some recipes to help you get started, we can help with that. Here are just a few of our favorites:
While the researchers suggested future studies should explore whether vitamin K supplements provide similar benefits, the evidence isn’t there yet. For now, focus on increasing your vitamin K intake by eating a variety of vitamin K-rich foods.
Our Expert Take
A new study in The American Journal of Clinical Nutrition suggests that higher dietary intake of vitamin K—specifically the vitamin K1 in leafy green vegetables—was associated with better lung function and a lower risk of developing COPD. These findings add to the growing body of research highlighting the benefits of adding more leafy greens to your diet. And if Popeye’s handful of raw spinach isn’t for you, don’t worry—there are plenty of other ways to get your vegetables in. Blend kale into a smoothie, stir spinach into soups or stews, roast broccoli or build a hearty salad with your favorite toppings. Small changes can make it easier to eat more leafy greens as part of an overall balanced diet.
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