The analysis, published in the British Journal of Nutrition, reviewed information from more than 168,000 people in 195 studies conducted in 44 countries - and is one of the first to investigate patterns of vitamin D status worldwide and in key population subgroups, using continuous values for 25(OH)D to improve comparisons.
Led by Dr Kristina Hoffmann from the Mannheim Institute of Public Health at Mannheim, Heidelberg University, Germany, the research team found that 37.3% of the studies reviewed reported mean serum vitamin levels - measured by 25-hydroxyvitamin D (25(OH)D) values - to be below 50 nmol/l; a value considered inadequate by health authorities worldwide.
"The strength of our study is that we used strict inclusion criteria to filter and compare data, using consistent values for 25(OH)D," said Hoffman. "Although we found a high degree of variability between reports of vitamin D status at the population level, more than one-third of the studies reviewed reported mean serum 25(OH)D values below 50 nmol/l."
Judy Stenmark, CEO of the International Osteoporosis Foundation (IOF) commented: "Given the global increase in the number of seniors and the almost fourfold increase in hip fractures due to osteoporosis since 1990, public health officials must address the impact of inadequate vitamin D status on fracture risk and overall health in their ageing populations as well as on children and adolescents.
"IOF urges further research as well as public health measures that would help to improve vitamin D status in these high-risk population groups."
The team, which included researchers from the IOF and DSM examined patterns of (25(OH)D) from the 195 studies in order to assess potential differences by age, sex and region.
"Vitamin D deficiency is associated with osteoporosis and is thought to increase the risk of cancer and CVD," said the team. "Despite these numerous potential health effects, data on vitamin D status at the population level and within key subgroups are limited."
Hoffman and her colleagues identified the 195 population-based studies - containing data from more than 168,000 people in 44 countries - using the Medline and EMBASE databases - finding that mean population-level 25(OH)D values varied considerably across the studies.
However, they noted that 37·3 % of the studies reported mean values below 50 nmol/l - a level that is generally classed as inadequate by health authorities worldwide.
"Although age-related differences were observed in the Asia/Pacific and Middle East/Africa regions, they were not observed elsewhere and sex-related differences were not observed in any region," added the team.
Further exploratory analyses did however suggest that newborns and institutionalised elderly from several regions worldwide appear to be at a generally higher risk of exhibiting lower 25(OH)D values, the authors said.
Other key findings from the study include:
- Vitamin D values were higher in North America than in Europe or the Middle-East.
- Only a limited number of studies for Latin America were available.
- Age-related differences were observed for the Asia-Pacific and Middle East regions, but not elsewhere.
- The substantial heterogeneity between the studies within each region precludes drawing conclusions on overall vitamin D status at the population level.
- There is a need for research designs which minimise potential sources of bias and thus strengthen understanding of vitamin D status in key subgroups worldwide.
Published online ahead of print, doi: 10.1017/s0007114513001840
"A systematic review of vitamin D status in populations worldwide"
Authors: Jennifer Hilger, Angelika Friedel, Raphael Herr, Tamara Rausch, Franz Roos, Denys A. Wahl, Dominique D. Pierroz, Peter Weber, Kristina Hoffmann