Seasonal variations in serum 25-hydroxy vitamin D levels in a Swedish cohort

Abstract

To study seasonal inter-individual and intra-individual variations in serum 25-hydroxy vitamin D (25(OH)D) and to explore parameters associated with 25(OH)D in a healthy Swedish adult population. 540 blood donors (60 % men; mean age 41 ± 13 years) and 75 thrombocyte donors (92 % men, aged 46 ± 11 years) were included. Serum was collected during 12 months and analyzed for 25(OH)D and parathyroid hormone (S-iPTH). The blood donors answered questionnaires concerning vitamin D supplements, smoking, physical activity, sunbed use and sun holidays. Repeated serum samples were collected from the thrombocyte donors to study the intra-individual variations in S-25(OH)D. S-25(OH)D varied greatly over the year correlating with the intensity of the UV-B irradiation (rS = 0.326; p < 0.001). During January–March, a S-25(OH)D level below the thresholds of 50 and 75 nmol/L was observed in 58 and 88 %, respectively, and during July–September in 11 and 50 % (p < 0.001). S-25(OH)D was negatively correlated with body mass index and S-iPTH, but was significantly higher in holiday makers in sunny destinations, sunbed users, non-smokers, and in the physically active. The intra-individual analyses showed a mean increase in S-25(OH)D by 8 nmol/L/month between April and August. Approximately 75 % had serum 25(OH)D values <75 nmol/L during 75 % of the year and 50 % had serum 25(OH)D <50 nmol/L during 50 % of the year. Serum 25(OH)D was strongly associated with parameters related to sun exposure, but only weakly with intake of vitamin D supplements.

Correlates of vitamin D in psychotic disorders: A comprehensive systematic review

“…This is perhaps not surprising since UVB irradiation intensity varies over the year and it is known that in healthy populations vitamin D levels change with UVB intensity. In one healthy sample participants were 55% deficient during January to March but the same sample was only 11% deficient between July and September, ( p<.001) (Klingberg et al, 2015). This highlights the importance to control for the season of blood sampling when comparing vitamin D levels across groups.…”

“Summer Shift”: A Potential Effect of Sunshine on the Time Onset of ST‐Elevation Acute Myocardial Infarction

“…Therefore, we computed the bimonthly—which, we again stress, helped to reduce the entropy originated by the higher sample rate of the monthly interval—Δ% signal for the overall (Finnish1+Finnish2=990 total individuals) Finnish population (Figure 4). And, in absence of Finnish data and without loss of generality (because Finland and Sweden are at the same latitude and there are no major climatic differences), we also plotted the average bimonthly vitamin D [more precisely the 25(OH)D serum levels] trend obtained from real data recently collected from a Swedish cohort 25. Interestingly, although the Finnish cohorts showed only a trend in the previous analysis (Figure 2A), here the Δ% signal reached (at least in the July‐August interval) a value lower than 50 that was the threshold previously suggested as a guideline for evidence of summer shift effect by the results in Figure 2B.…”

“…The result was a Spearman correlation −0.71 between the bimonthly Δ% in the overall Finnish cohort and the average bimonthly levels of serum vitamin D in a reference Swedish cohort 25. The monthly Δ% in the overall Finnish cohort presented noise (see Figure 5) that affected the estimation of the bimonthly Δ% trend used to compute the correlation with bimonthly vitamin D. Therefore, we performed an advanced analysis, and in order to estimate a noise‐reduced monthly Δ% time series signal, we applied a nonlinear adaptive filter—the median modified Wiener filter star26—for noise reduction and signal smoothing to the raw monthly Δ% (Figure 5).…”

High levels of vitamin D associated with less ischemic heart disease – a nested case-control study among rural men in Sweden

“…Additional sources are natural dietary content, vitamin food fortification and supplements. The latitude of geographical location is of importance for obtaining sufficient sunlight for the synthesis of active vitamin D. Seasonal variation in vitamin D levels have been illustrated in the Nordic countries [14,15] and in the United Kingdom where high prevalence of deficient vitamin D levels have been found during winter and spring [16]. In the Nordic countries, exposure to the sun is below critical level for half of the year.…”