To the Editor 27th January 2008-01-26

The recent on-line publication by Rintamaki et al. [1] reports associations of seasonal variations in mood and behaviour with abnormalities of the variables used to define the ‘metabolic syndrome’ with its associated risks of type 2 diabetes [TDM] and its sequelae including cardiovascular disease. Any factor capable of worsening the risk of these conditions is of importance in view of the increasing prevalence of T2DM currently being seen on a world-wide basis [2]. Rintamaki et al. postulate a role for inherent circadian clockwork systems as an explanation of the associations of variation in severity of the abnormalities used to define metabolic syndrome with season. There is, however, considerable evidence available to suggest that variations in glycemia, insulin secretion, insulin resistance, blood pressure and lipid abnormalities are associated with variations in vitamin D status [3-6]. Additionally, vitamin D status varies with season, being highest after the summer months and lowest at the end of the winter in every population group where there are variations in incident ultraviolet light capable of inducing vitamin D synthesis in the skin and hypovitaminosis D is increasingly well recognized world-wide [7]. There are bound to more seasonal effects on human biology than those of vitamin D availability alone but such factors could well be shown to be independent of vitamin D status since the latter with dietary and supplemental vitamin D intake as well as with seasonal UVb availability, in Denmark as elsewhere since current supplementation can improve but does not eliminate the problem in that country [8]. Furthermore, hypovitaminosis D has been linked to depression, behavioural problems and seasonal affective disorder though supplementation at the modest doses used to date (400-800 IU daily) has not always led to their improvement [8-14]. These findings make it important to enquire whether the authors have examined the predictive association between season and their findings on metabolic syndrome variables for independence from the vitamin D status of their subjects. If not, the measurement of serum 25-hydroxyvitamin D, generally accepted to reflect vitamin D repletion, in this cohort would be of considerable importance.


1. Rintamaki R, Grimaldi S, Englund A, Haukka J, Paronen T, Reunanen A, Aromaa A, Lonnnqvist J. (2008) Seasonal changes in mood and behaviour are linked to metabolic syndrome. PLoS ONE 3(1):e1482.www.plosone.org
2. Bonow RO, Gheorghiade M. (2004) The diabetes epidemic: a national and global crisis. Am J Med. 116 Suppl 5A:2S-10S. Review.
3. Boucher BJ. Inadequate vitamin D status: does it contribute to the disorders comprising syndrome 'X'? (1998) Br J Nutr. 79:315-27. Review.
4. Chiu KC, Chu A, Go VL, Saad MF. Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction. (2004) Am J Clin Nutr. 79:820-5.
5. Baynes KC, Boucher BJ, Feskens EJ, Kromhout D. Vitamin D, glucose tolerance and insulinaemia in elderly men. (1997) Diabetologia. 40:344-7.
6. John WG, Noonan K, Mannan N, Boucher BJ. Hypovitaminosis D is associated with reductions in serum apolipoprotein A-I but not with fasting lipids in British Bangladeshis. (2005) Am J Clin Nutr. 82:517-22.
7. Calvo MS, Whiting SJ, Barton CN. (2005), Vitamin D intake: a global perspective of current status. In Symposium: Vitamin D insufficiency: a significant risk factor in chronic disease and potential disease-specific biomarkers of vitamin D sufficiency. J Nutr. 135:310-16
8. Andersen R, Mølgaard C, Skovgaard LT, Brot C, Cashman KD, Chabros E, Charzewska J, Flynn A, Jakobsen J, Kärkkäinen M, Kiely M, Lamberg-Allardt C, Moreiras O, Natri AM, O'Brien M, Rogalska-Niedzwiedz M, Ovesen L. (2005) Teenage girls and elderly women living in northern Europe have low winter vitamin D status. Eur J Clin Nutr. 59:533-41.
9. Stumpf WE, Privette TH. (1989). Light, vitamin D and psychiatry. Role of 1,25 dihydroxyvitamin D3 (soltriol) in etiology and therapy of seasonal affective disorder and other mental processes. Psychopharmacology (Berl). 97:285-94
10. Harris S, Dawson-Hughes B. (1993). Seasonal mood changes in 250 normal women. Psychiatry Res. 49:77-87
11. Landsdown AT, Provost SC. (1998). Vitamin D3 enhances mood in healthy subjects during the winter. Psychopharmacology (Berl). 135:319-23
12. Dumville JC, Miles JN, Porthouse J, Cockayne S, Saxon L, King C. (2006). Can vitamin D supplementation prevent winter blues? A randomized trial among older women. J Nutr Health Ageing 10:151-3
13. Wilkins CH, Sheline YI, Roe CM, Birge SJ, Morriis JV (2006). Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. Am J Geriatr Psychiatry. 14:1032-40.
14. Berk M, Sanders KM, Pasco JA, Jacka FN, Williams LJ, Hayles AL, Dodd S. (2007) Vitamin D deficiency may play a role in depression. Med Hypotheses. 69:1316-9

Barbara J Boucher MD, FRCP
Centre for Diabetes & Metabolic Medicine
Barts & the London Medical and Dental School, London. UK
E-mail bboucher@doctors.org.uk