India, Sept. 19 -- India is a land of bright skies and long summers, yet beneath the sunshine lies a widespread problem: more than three out of four Indians are Vitamin D deficient or have insufficient levels. The symptoms are usually vague: a general feeling of tiredness, sudden muscle cramps, niggling bone pain, and low mood. It's a paradox playing out in clinics and homes across the country. Most parts of the country get plenty of sunlight year-round. Yet, people complain of bones quietly losing strength, leading to osteopenia, osteoporosis, and fractures later in life.

The reasons are deeply human, deeply mundane. Many of us spend most of our day indoors sitting at desks in cubicles at work, in classrooms, and in our cars commuting t...