Objective Lay interest in vitamin D and the potential benefits of supplementation is considerable, but little information exists concerning lay knowledge, beliefs and attitudes towards vitamin D to inform public health initiatives and professional guidance.

Design Qualitative focus group study.

Participants 58 adults capturing diversity in disease status, gender, age and ethnicity.

Setting A large general practice in east London.

Results Many respondents lacked knowledge about vitamin D, including dietary sources and government recommendations. Most were positive about sun exposure, but confused by ambiguous health messages about risks and benefits of sunshine. Medicalised views of vitamin D were prominent, notably from those in favour of supplementation, who talked of “doses”, “side effects” and “regular testing.” Fortification of food with vitamin D was controversial, with opposing utilitarian (better overall for the majority) and libertarian (freedom to choose) views.

Conclusions Knowledge about vitamin D was limited. Clearer messages are needed about risks and benefits of sun exposure. Testing and supplementation by health professionals, while potentially useful in some high-risk groups, have contributed to a medicalised view of vitamin D. Health policy should address the public's need for clear information on sources and effects of vitamin D, including risks and benefits of sun exposure, and take account of divergent views on fortification. Professional guidance is needed on testing and supplementation to counter inappropriate medicalisation.