If you’re an egg whites–only guy, think about changing your order. A study in the European Journal of Preventive Cardiology suggests that vitamin D—which is found in free-range egg yolks—may boost lung health.
Cardiorespiratory fitness, or the ability of the heart, lung, and muscle cells to use oxygen efficiently, is a marker of overall health and fitness. In blood and fitness tests, for every small increase of vitamin D a person had, there was an uptick in VO2 max. While the study did not determine an optimal level of the vitamin, people living in places with less sun exposure should load up on egg yolks and other vitamin D–rich foods, like fatty fish and fortified cereal.