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Table 1 Characteristics of included studies

From: Association between micronutrient deficiency and acute respiratory infections in healthy adults: a systematic review of observational studies

Author, Year [Ref.]Reported Study DesignCountry of study; follow-up durationPopulation size and description (% Men); Mean Age (years);Micronutrient in questionCut-offs for different micronutrient categories, as defined by study (nmol/L)Outcome reported
DeficientInadequateSufficientOptimal
Met inclusion criteria clearly
Laaksi, 2007 [19]Prospective cohortFinland; 6 months756 Young Finnish military conscripts (100%); 18–29*Vitamin D<40≥40• Clinical RTI incidence
• RTI duration
He, 2013 [17]Prospective cohortUK; 4 months225 healthy endurance exercise athletes with ≥3 h of total moderate/high-intensity training per week (69.8%); 21Vitamin D12 to 3030 to 5050 to 120≥120• Self-reported upper RTI incidence
• Self-reported upper RTI duration
• Subjective symptom severity per episode
Jovanonich, 2014 [18]Retrospective case-controlUS; 3–15 months132 patients hospitalised for pneumonia (cases) or other reasons (controls) (29%); 60Vitamin D< 3737 to 5051 to 75> 75• Laboratory-confirmed pneumonia incidence
Rafiq, 2018 [20]Cross sectionalNetherlands; 1 month prior to interview6138 men and women living in the greater area of Leiden with self-reported BMI ≥27 kg/m2 (43.9%); 55 (deficient), 55.9 (inadequate), 55.7 (sufficient)Vitamin D< 5050 to 75≥75• Self-reported common cold incidence
Highly likely to meet inclusion criteria
Sabetta, 2010 [24]Prospective cohortUS; 4 months198 healthy adults (42.9%); 20–88*Vitamin D< 95≥95• Clinical acute viral RTI incidence
• Acute viral RTI duration
Berry, 2011 [21]Cross sectionalUK; 3 weeks prior to interview6789 non-pregnant free-living Caucasians born in England, Scotland and Wales during a week in March 1958 (birth cohort) (49.9%); 45Vitamin D< 2525 to 49.950 to 74.975 to 99.9≥100• Self-reported influenza, pneumonia, bronchitis or severe cold incidence
Nanri, 2017 [23]Nested Case-controlJapan; 6 months532 employees from 4 companies in Kanto and Tokai regions (83.1%); 37.6Vitamin D< 5050 to < 75≥75• Clinical influenza incidence
Lee, 2018 [22]Retrospective cross sectionalUS; 1 year post-vaccination437 Young, healthy US military members vaccinated with 2009 monovalent influenza A (H1N1) vaccine (50.3%); Not reported by 90.6% of the population were 19–39 years oldVitamin D< 5050 to 75> 75• Clinical influenza-like illness incidence
  1. RTI Respiratory tract infections, UK United Kingdom, US United States of America, *age range