The National Institute for Public Health says that vitamin D deficiency is common among Slovenians in winter. The institute recommends that people supplement with vitamin D during the winter.
A national study has shown that around 80% of Slovenia's adult population is deficient and around 40% are severely deficient.
People in nursing homes or who are mostly indoors between 10am and 4pm should take the supplement throughout the year.
Women should also take vitamin D before and during pregnancy and when breastfeeding, the institute said, adding that vitamin D is also recommended for children.