Don’t get sunburned! We hear that constantly. But here’s a statement you don’t hear often: Don’t use sunscreen. According to a new study published in The Journal of the American Osteopathic Association, using sunscreen could be one of our worst habits.

The researchers came to their conclusions after conducting a review of clinical studies of the different causes of vitamin D deficiency. According to the team, using sunscreen with an SPF of 15 or higher can reduce the body’s vitamin D3 production by 99%!

This is bad enough for everyone, but it’s especially a problem for patients with Crohn’s disease, diabetes, or chronic kidney disease. That’s because patients with these diseases already have a problem with maintaining a healthy vitamin D level. The researchers were able to show that sunscreen use in patients with these diseases causes almost one million cases of vitamin D deficiency worldwide. And what does vitamin D deficiency lead to? It’s not pretty.

Vitamin D is critical for healthy bones. A deficiency leads to decreased bone density, osteoporosis, and fractures. The vitamin is also vital for optimal muscle and nerve function. And it helps the immune system to stave off infection. Not only that, but low levels of vitamin D also can cause cancer, rickets, bone pain, muscle weakness, increased blood pressure, depression, and multiple sclerosis.