Monthly ambient sunlight, infections and relapse rates in multiple sclerosis.
BACKGROUND
Monthly variation in multiple sclerosis (MS) relapses has been found. The relationship between seasonal environmental factors, infections, serum vitamin D [25(OH)D] and MS relapses is undetermined.


METHODS
We prospectively followed a population-based cohort of relapsing-remitting (RR) MS patients in Southern Tasmania for a mean 2.3 years (January 2002-April 2005). Associations between monthly ambient environmental factors, estimated serum 25(OH)D, upper respiratory tract (URT) infections and relapse rates were examined using weighted Pearson's correlation and linear regression.


RESULTS
Of 199 definite MS patients, 142 had RRMS. The lowest relapse rate of 0.5 per 1,000 days (95% CI: 0.2-1.3) occurred in February (mid-late summer) versus the March-January RR of 1.1 per 1,000 days (95% CI: 0.9-1.3; p = 0.018, weighted regression). Monthly relapse rates correlated with: (1) prior erythemal ultraviolet radiation (EUV): lagged 1.5 months, r = -0.32, p = 0.046; (2) URT infection rate: no lag, r = 0.39, p = 0.014; (3) 25(OH)D: no lag, r = -0.31, p = 0.057. The association between URT infections and relapses was reduced after adjustment for monthly EUV.


CONCLUSIONS
Relapse rates were inversely associated with EUV and serum 25(OH)D levels and positively associated with URT infections. The demonstrated lag between EUV but not 25(OH)D and relapse rates is consistent with a role for EUV-generated 25(OH)D in the alteration of relapse rates. Future work on the association between URT infections and relapses should be considered in the context of ultraviolet radiation and vitamin D.
Tremlett
Helen
H
Faculty of Medicine (Neurology), University of British Columbia, Vancouver, B.C., Canada. tremlett@interchange.ubc.ca
van der Mei
Ingrid A F
IA
Pittas
Fotini
F
Blizzard
Leigh
L
Paley
Glenys
G
Mesaros
Desiree
D
Woodbaker
Richard
R
Nunez
Manuel
M
Dwyer
Terence
T
Taylor
Bruce V
BV
Ponsonby
Anne-Louise
AL
D000328:Adult; D017668:Age of Onset; D000368:Aged; D005260:Female; D006801:Humans; D007239:Infections / Q000453:epidemiology*; D016899:Interferon-beta / Q000627:therapeutic use; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000188:drug therapy / Q000453:epidemiology* / Q000503:physiopathology / Q000517:prevention & control; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000188:drug therapy / Q000453:epidemiology* / Q000517:prevention & control; D011446:Prospective Studies; D012008:Recurrence; D012044:Regression Analysis; D013472:Sunlight; D013781:Texas; D055815:Young Adult
D016899:Interferon-beta