A big problem is that the range that we have decided to call “normal” might not actually be a normal range.

For example, 50% of surfers were found to have insufficient vitamin D in one study. https://pubmed.ncbi.nlm.nih.gov/17426097/

There are at least two possible conclusions that you could draw. One conclusion is that we all need vitamin D supplementation regardless of how much sun exposure we receive.

Another conclusion is that we might want to reevaluate what we consider the normal range to be, especially when we are deciding a range for a specific individual.

No, the conclusion is surfers are conscious of their exposure and wear sun protection.