Would John Muir not likely have a vitamin D deficiency?
Think slowly and carefully, before giving your answer.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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John Muir frequently spent time exploring various places in nature. Spending time in nature increases your exposure to sunlight. Skin exposure to sunlight increases vitamin D levels in the body.
So, the answer is yes.