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To be more explicit about it being "easily fixed", here's a quote:

Asked for a general recommendation, Dr. Holick suggests going outside in summer unprotected by sunscreen (except for the face, which should always be protected) wearing minimal clothing from 10 a.m. to 3 p.m. two or three times a week for 5 to 10 minutes.

That's all it takes to fix the "problem"