Taking a brisk walk in the sun can do more than just boost your mood—it can help your smile appear sunnier, too. “It only takes about five to 10 minutes of sunshine to get a dose that generates about 10,000 IUs of vitamin D, which is essential for bone and dental health,” explains Charles F. Hildebolt, professor emeritus of radiology at Washington University School of Medicine, in St. Louis, MO. The flip side: When your body doesn’t get enough vitamin D from the sun, food, or supplements, your teeth can develop gaps or bubbles in the dentin, the layer under the enamel that’s responsible for most of the tooth’s structure.

However, shorter days can mean even doing your daily cardio outside might not be enough to keep your pearly whites healthy, says Hildebolt— especially for those who live at northern latitudes, where the sun’s UV rays aren’t sufficient to produce vitamin D. So consider taking a daily vitamin D supplement (aim for at least 600 IUs) or having fortified foods like eggs, cereal, or D-fortified milk and juice to keep your whole skeleton strong.