Friday is the 12th annual National Wear Red Day, so there’s a reason you may have spotted some people sporting the color today.

Every year, the first Friday in February is designated as a day when people wear red to show support against heart disease, which is the No. 1 killer in woman, ABC World News noted.

According to the American Heart Association, 1 in 3 woman will die of heart disease or a stroke. And, many Americans have several of the risk factors associated with each including diabetes, high cholesterol and high blood pressure.

The association hopes that the annual National Wear Red Day will continue to raise awareness about something that affects so many people.

Both the hashtags #WearRedDay and #GoRed have trended on Twitter and some are taking selfies of themselves posing in red.

USA Today reported that the color choice reflects not only what everyone associates with hearts, but the color of a human heart. And by going red on this day you show your full support of helping put an end to this preventable disease.