"Low serum levels of vitamin D are found in significant numbers of all population groups in the UK: in winter 30-40% of all age groups in the general population are classed as vitamin D deficient. Even towards the end of summer 8% of adults and 13% of adolescents remain deficient."
where deficient is defined as < 25 nmol/L of 25(OH)D
This is part of a series of ongoing projects that have received NIH funding over the last 7 years. Ecohealth, in turn, funds WIV: https://www.nature.com/articles/d41586-020-02473-4