{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,1]],"date-time":"2026-06-01T13:03:20Z","timestamp":1780319000889,"version":"3.54.1"},"reference-count":40,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2014,7,9]],"date-time":"2014-07-09T00:00:00Z","timestamp":1404864000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>The early indications of vitamin C deficiency are unremarkable (fatigue, malaise, depression) and may manifest as a reduced desire to be physically active; moreover, hypovitaminosis C may be associated with increased cold duration and severity. This study examined the impact of vitamin C on physical activity and respiratory tract infections during the peak of the cold season. Healthy non-smoking adult men (18\u201335 years; BMI &lt; 34 kg\/m2; plasma vitamin C &lt; 45 \u00b5mol\/L) received either 1000 mg of vitamin C daily (n = 15) or placebo (n = 13) in a randomized, double-blind, eight-week trial. All participants completed the Wisconsin Upper Respiratory Symptom Survey-21 daily and the Godin Leisure-Time Exercise Questionnaire weekly. In the final two weeks of the trial, the physical activity score rose modestly for the vitamin C group vs. placebo after adjusting for baseline values: +39.6% (95% CI [\u22124.5,83.7]; p = 0.10). The number of participants reporting cold episodes was 7 and 11 for the vitamin C and placebo groups respectively during the eight-week trial (RR = 0.55; 95% CI [0.33,0.94]; p = 0.04) and cold duration was reduced 59% in the vitamin C versus placebo groups (\u22123.2 days; 95% CI [\u22127.0,0.6]; p = 0.06). These data suggest measurable health advantages associated with vitamin C supplementation in a population with adequate-to-low vitamin C status.<\/jats:p>","DOI":"10.3390\/nu6072572","type":"journal-article","created":{"date-parts":[[2014,7,9]],"date-time":"2014-07-09T11:18:18Z","timestamp":1404904698000},"page":"2572-2583","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":61,"title":["Vitamin C Supplementation Slightly Improves Physical Activity Levels and Reduces Cold Incidence in Men with Marginal Vitamin C Status: A Randomized Controlled Trial"],"prefix":"10.3390","volume":"6","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9540-6860","authenticated-orcid":false,"given":"Carol","family":"Johnston","sequence":"first","affiliation":[{"name":"School of Nutrition and Health Promotion, Arizona State University, 500 N. 3rd St.,  Phoenix, AZ 85004, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gillean","family":"Barkyoumb","sequence":"additional","affiliation":[{"name":"Isagenix\u00ae International LLC, 2225 S. Price Rd., Chandler, AZ 85286, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sara","family":"Schumacher","sequence":"additional","affiliation":[{"name":"Cancer Treatment Centers of America\u00ae, 14200 W. Celebrate Life Way, Goodyear, AZ 85338, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2014,7,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"957S","DOI":"10.3945\/jn.112.173021","article-title":"Dietary supplement use and smoking are important correlates of biomarkers of water-soluble vitamin status after adjusting for sociodemographic and lifestyle variables in a representative sample of U.S. adults","volume":"143","author":"Pfeiffer","year":"2013","journal-title":"J. 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