According to a 2010 infographic by Information is Beautiful, people inhabiting in the Northern hemisphere, more precisely above latitude 42°N, are not getting enough UVB light from sunlight to make vitamin D in the skin during winter season.
In the UK, 50% of the population has insufficient levels of vitamin D, while 16% of the population is severely deficient. In the United States, 77% of the population has insufficient levels of vitamin D, while 6% of the population is severely deficient. Within the U.S., the groups more affected by insufficient levels of vitamin D are Non-Hispanic blacks (98%) and Mexican Americans (90%).
To try compensate for the lack of UVB light in winter time and the consequent low vitamin D levels, consumers have turned to the vitamin D industry, an industry that is worth $460 million, as of 2009, in the U.S. alone.
For more graphics and statistics, visit: Information is Beautiful: Vitamin D