Vitamin D deficiency is considered a worldwide pandemic. In fact, researchers estimate that up to ⅓ of the world’s population is vitamin D deficient, with an even higher prevalence in some regions.
Due to the lack of knowledge regarding the prevalence of vitamin D deficiency in southern Europe, researchers recently conducted a systematic review of 107 studies to provide clarity on the matter.
The researchers included observational studies published after 1990 and utilized the following inclusion criteria:
- Studies had well-defined/characterized samples of healthy subjects.
- Studies were conducted with randomly selected subjects from the general population or population subgroups stratified by age, sex and specific areas within France, Italy, Spain, Portugal, Greece, Malta, Cyprus, Turkey and Israel.
- Studies reported mean values of serum 25(OH)D concentrations and/or prevalence data on serum 25(OH)D below one or more of the following thresholds: : <10 ng/ml (25 nmol/l), <12 ng/ml (30 nmol/l), <15 ng/ml (37.5 nmol/l), <20 ng/ml (50 nmol/l) and <30 ng/ml (75 nmol/l).
- Studies provided details on assay used for assessment of serum 25(OH)D concentrations.
- Studies reported season(s) in which blood sampling within the study occurred.
The researchers also evaluated the 630,093 participants based on the following age categories: neonates/infants (0–1 years), children/adolescents (> 1–18 years), adults (> 18–65 years) and elderly (> 65 years).
This is what the researchers found:
- A total of 35 studies were conducted in Italy, 20 in Spain, 19 in Turkey, 12 in France, 11 in Israel, 5 in Greece, 2 in Cyprus, 1 in Portugal and 2 studies evaluated more than one of the southern European countries.
- Vitamin D status in neonates/infants ranged from 5.68 ng/ml (14.2 nmol/l) to 40.4 ng/ml (101 nmol/l).
- Average prevalence of vitamin D status below 10 ng/ml (25 nmol/l) in neonates/infants was approximately 20%.
- For adolescents, vitamin D status ranged from 8.68 ng/ml (21.7 nmol/l) to 40.4 ng/ml (101 nmol/l).
- Average prevalence of vitamin D status below 10 ng/ml (25 nmol/l) in adolescents was approximately 27%
- The lowest value of vitamin D status in adults was 13.68 ng/ml (34.2 nmol/l) while the highest value was 42.89 ng/ml (107.2 nmol/l).
- Average prevalence of vitamin D status below 10 ng/ml (25 nmol/l) in adults was approximately 16%.
- Vitamin D status ranged from 2.4 ng/ml (6 nmol/l) to 63.2 ng/ml (158 nmol/l) in the elderly.
- Average prevalence of vitamin D status below 10 ng/ml (25 nmol/l) in the elderly was approximately 16%.
The researchers concluded:
“Despite the abundance of solar UVB radiation in southern Europe and eastern Mediterranean region, more than one-third of the studies identified by the present systematic review reported mean 25(OH)D levels below 50 nmol/L and of those studies that reported the prevalence of serum 25(OH)D < 25 nmol/L in all seasons, between 16 and 27% of study participants, on average, were deficient on this basis, depending on the age group.”