J Epidemiol Community Health. 2015 Apr;69(4):388-92. doi: 10.1136/jech-2014-204632. Epub 2015 Jan 6.
Klenk J1, Rapp K2, Denkinger M3, Nagel G4, Nikolaus T3, Peter R4, Boehm BO5, Koenig W6, Rothenbacher D4; ActiFE Study Group.
Decades ago a flawed study estimated that no Vitamin D would be produced in the winter above latitude 37 degrees. That study lowered the UV intensity setting until no more vitamin D was produced, then calculated the latitude which was equal to that setting. The flaw was that the participants already had high enough levels of vitamin D. A much better study would have increased the UV intensity until vitamin D was produced.
Map of Vitamin D Winter - from the web
The study on this page looked at the amount of walking by German seniors
at latitude 48 degrees North (London, Calgary = 51 N)
Walking was measured for just 1 week - not for each season
Compared differences in vitamin D levels between those walking a lot vs a little
2.6 hour vs 1 hour
PDF was purchased and scanned
Possible errors in the study
- Those who walked more did so because they were healthier because they already had more vitamin D
- Those who walked more were younger (73 vs 79)
- Those who walked more were less obese (12% vs 38%: BMI> 30)
- Only a single measurement of walking time was taken - NOT at each season
However, many people feel very recharged by getting outdoors even when current belief says there is so little UV that no vitamin D should be generated
See also VitaminDWiki
- UV, sunshine, and vitamin D (87 charts) - Holick March 2013
- Small amounts of UV result in increased vitamin D levels – March 2012
- Is there really a UV winter
- Vitamin D - Facts and Myths Vitamin D Winter is myth #1
- Map of Jan minutes to get same amount of vitamin D
To analyse the seasonal relationship of objectively measured physical activity with vitamin D status in older persons from Southern Germany (latitude: 48.4°N).
Physical activity was assessed in 1193 community-dwelling individuals aged ≥65 years (58% men) over 1 week using a thigh-worn accelerometer. Furthermore, the 25-hydroxyvitamin D (25(OH)D) level was measured. Least-square means of 25(OH)D serum levels were calculated for quartiles of average daily walking duration stratified by season and adjusted for gender, age and body mass index. Participants with prescribed vitamin D supplements were excluded.
Statistically significant linear associations between quartiles of walking duration with 25(OH)D serum levels were observed in all seasons but not in summer. Differences in 25(OH)D serum levels between the first and the last quartile were 3.42 ng/mL (p=0.002) in winter, 2.80 ng/mL (p=0.009) in spring, and 3.60 ng/mL (p<0.001) in the fall. The proportion of vitamin D insufficiency (<20 ng/mL) even in the highest quartile of walking duration was 45.3% in winter, 73.7% in spring, 17.4% in summer and 16.5% in the fall.
Although a positive dose-response relationship was seen between walking duration and the 25(OH)D serum level for most seasons, vitamin D insufficiency was still very prevalent even in high-active persons during all seasons.
Published by the BMJ Publishing Group Limited.
References include previous similar studies
- Florez H, Martinez R, Chacra W, et al. Outdoor exercise reduces the risk of hypovitaminosis D in the obese. J Steroid Biochem Mol Biol 2007;103:679–81.
- Scragg R, Camargo CA Jr. Frequency of leisure-time physical activity and serum 25-hydroxyvitamin D levels in the US population: results from the Third National Health and Nutrition Examination Survey. Am J Epidemiol 2008;168:577–86; discussion 587–591.
- Hintzpeter B, Mensink GBM, Thierfelder W, et al. Vitamin D status and health correlates among German adults. Eur J Clin Nutr 2008;62:1079–89.
- Brock K, Huang W-Y, Fraser DR, et al. Low vitamin D status is associated with physical inactivity, obesity and low vitamin D intake in a large US sample of healthy middle-aged men and women. J Steroid Biochem Mol Biol 2010;121:462–6.
- Kluczynski MA, Lamonte MJ, Mares JA, et al. Duration of physical activity and serum 25-hydroxyvitamin D D status of postmenopausal women. Ann Epidemiol 2011;21:440–9.