Effects of a healthy Nordic diet on plasma 25-hydroxyvitamin D concentration in subjects with metabolic syndrome: a randomized, placebo-controlled trial (SYSDIET)

Research output: Contribution to journalArticle


At northern latitudes, vitamin D is not synthesized endogenously during winter, causing low plasma 25-hydroxyvitamin D (25(OH)D) concentrations. Therefore, we evaluated the effects of a healthy Nordic diet based on Nordic nutrition recommendations (NNR) on plasma 25(OH)D and explored its dietary predictors. In a Nordic multi-centre trial, subjects (n = 213) with metabolic syndrome were randomized to a control or a healthy Nordic diet favouring fish (a parts per thousand yen300 g/week, including a parts per thousand yen200 g/week fatty fish), whole-grain products, berries, fruits, vegetables, rapeseed oil and low-fat dairy products. Plasma 25(OH)D and parathyroid hormone were analysed before and after 18- to 24-week intervention. At baseline, 45 % had vitamin D inadequacy (< 50 nmol/l), whereas 8 % had deficiency (< 25 nmol/l). Dietary vitamin D intake was increased by the healthy Nordic diet (P < 0.001). The healthy Nordic and the control diet reduced the prevalence of vitamin D inadequacy by 42 % (P < 0.001) and 19 % (P = 0.002), respectively, without between-group difference (P = 0.142). Compared with control, plasma 25(OH)D (P = 0.208) and parathyroid hormone (P = 0.207) were not altered by the healthy Nordic diet. Predictors for 25(OH)D were intake of vitamin D, eicosapentaenoic acids (EPA), docosahexaenoic acids (DHA), vitamin D supplement, plasma EPA and plasma DHA. Nevertheless, only vitamin D intake and season predicted the 25(OH)D changes. Consuming a healthy Nordic diet based on NNR increased vitamin D intake but not plasma 25(OH)D concentration. The reason why fish consumption did not improve vitamin D status might be that many fish are farmed and might contain little vitamin D or that frying fish may result in vitamin D extraction. Additional ways to improve vitamin D status in Nordic countries may be needed.


  • Lea Brader
  • Lars Rejnmark
  • Carsten Carlberg
  • Ursula Schwab
  • Marjukka Kolehmainen
  • Fredrik Rosqvist
  • Lieselotte Cloetens
  • Mona Landin-Olsson
  • Ingibjorg Gunnarsdottir
  • Kaisa S. Poutanen
  • Karl-Heinz Herzig
  • Ulf Riserus
  • Markku J. Savolainen
  • Inga Thorsdottir
  • Matti Uusitupa
  • Kjeld Hermansen
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Nutrition and Dietetics


  • Vitamin D, 25-hydroxyvitamin D, Healthy Nordic diet, Nordic nutrition, recommendations, Metabolic syndrome
Original languageEnglish
Pages (from-to)1123-1134
JournalEuropean Journal of Nutrition
Issue number4
Publication statusPublished - 2014
Publication categoryResearch