What is the most common cause of vitamin D deficiency? What was the nature of John Muir's life's work? Does #2 ensure that he does not experience #1?
John Muir
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.
Scottish-born American naturalist and author
Would John Muir not likely have a vitamin D deficiency?