who averaged 15 hours per week in the sun over the last three months. Their Vitamin D levels were as low as 11 ng/ml, which is severely deficient. [17] Findings like this have led some to speculate that water sports, bathing, and showering, may make our skin less able to absorb Vitamin D.
https://www.huffpost.com/entry/why-would-i-be-low-in-vitamin-d_b_8546144