In the study, people who consumed daily lutein supplements over the course of a year improved their sharpness of vision, contrast sensitivity, and sensitivity to glare—all markers that can result in better nighttime driving. Lutein is found in healthy eye tissue in your retina and is responsible for how sharply you can see. But if your lutein is low—potential culprits include a poor diet, smoking, and exposure to UV light—your vision starts to go, especially in dimly lit or glary situations. (Keep your peepers healthy with these 6 ways to age-proof your eyes.) The 20 milligrams (mg) of lutein that people consumed every day is about the same as 1 cup of cooked kale (about 4 cups raw)—not exactly a small amount to consume daily. But a diet rich in a variety of fruits and vegetables will help you consume optimal levels of the nutrient, suggests a study from the University of Texas. However, if you’re looking to sharpen your vision, you may need to take a supplement to really see the effects. More from Men’s Health: What Your Eyes Say About Your Brain