Evolution of Serum 25OHD in Response to Vitamin D3-Fortified Yogurts Consumed by Healthy Menopausal Women: A 6-Month Randomized Controlled Trial Assessing the Interactions between Doses, Baseline Vitamin D Status, and Seasonality

Abstract

Background: Adequate vitamin D status contributes to bone fragility risk reduction and possibly other pathological conditions that occur with aging. In response to pharmaceutical vitamin D₃ supplements, several studies have documented the influence of doses, baseline status, and seasonality on serum 25-hydroyvitamin D (s25OHD).

Objective: Using fortified yogurt, we investigated in one randomized controlled trial how both baseline status, as assessed by measuring s25OHD prior the onset of the trial, and the season of enrollment quantitatively influenced the response to the supplemented (Suppl.) of vitamin D₃ (VitD₃) in healthy community-dwelling women.

Methods: A 24-week controlled trial was conducted in menopausal women (mean age: 61.5). Participants were randomized into 3 groups (Gr): Gr.Suppl.0, time controls maintaining dietary habits; Gr.Suppl.5 and Gr.Suppl.10 consuming one and two 125-g servings of VitD₃-fortified yogurts with 5- and 10-µg daily doses, respectively. The 16 intervention weeks lasted from early January to mid-August, the 8 follow-up weeks, without product, from late August to mid-October. Before enrollment, subjects were randomized into 2 s25OHD strata: low stratum (LoStr): 25-50 nmol/L; high stratum (HiStr): >50-75 nmol/L.

Results: All enrolled participants adhered to the protocol throughout the 24-week study: Gr.Suppl.0 (n = 45), Gr.Suppl.5 (n = 44), and Gr.Suppl.10 (n = 44). Over the 16 intervention and 8 follow-up weeks, s25OHD increased in both supplemented groups, more in Gr.Suppl.10 than in Gr.Suppl.5. At the end of the intervention, the subject proportion with s25OHD ≥ 50 nmol/L was 37.8, 54.5, and 63.6% in Gr.Suppl.0, Gr.Suppl.5, and Gr.Suppl.10, respectively. The constant rate of s25OHD per supplemental VitD₃ microgram was greater in LoStr than HiStr. The s25OHD increase was greater with late (mid-March) than early (mid-January) inclusion.

Conclusion: This randomized trial demonstrates (1) a dose-dependent s25OHD improvement related to fortified yogurt consumption; (2) an inversely baseline-dependent increase in s25OHD; and (3) a seasonal effect that highlights the importance of VitD₃-fortified foods during winter, even at 5 µg/d, in healthy menopausal women.

Keywords: Nutritional intervention; menopausal women; seasonality interaction; serum 25OHD dose–response; vitamin D3–fortified yogurts.

Figure 1A.

Change (∆) in s25OHD in nanomoles per liter from baseline to weeks 4, 8, 12, and 16 after the onset of the intervention. One hundred thirty-three healthy menopausal women were randomized into 3 groups: Gr.Suppl.0, who were advised not to change their dietary habits; Gr.Suppl.5, who consumed one fortified yogurt that provided 5 µg of vitamin D₃ per day; and Gr.Suppl.10, who consumed 2 fortified yogurts that provided 10 µg of vitamin D₃ per day. The SD values are written in association with each column. Statistical test by repeated measures ANOVA indicates that the differences between Gr.Suppl.5 or Gr.Suppl.10 and Gr.Suppl.0 was significant at p = 0.0007 and p = 0.00002, respectively. The difference between Gr.Suppl.5 and Gr, Suppl.10 was not significant taking into account an adjustment for 3 comparisons reducing the p level from 0.050 to 0.0167.

Figure 1B.

Proportion of subjects whose s25OHD increased to ≥50 nmol/L from baseline to the end of the intervention (WK16) and 8 weeks later (WK24). The figure illustrates a dose effect related to the duration of the intervention from BSL to WK16. The seasonality effect is highlighted by the increase in the time-controlled group (Gr.Suppl.0) from BSL (samples collected on average from mid-January to mid-March 2015) to WK24 (samples collected on average from mid-July to mid-August 2015). The corresponding absolute values (mean ± SD) of s25OHD in nanomoles per liter are presented in Figure 1A. The probability of difference as assessed by chi-squared tests was p = 0.002 and p = 0.088 between Gr.Suppl.0 and Gr.Suppl.5 at WK8 and WK16, respectively, and p = 0.0001 and p = 0.008 between Gr.Suppl.0 and Gr.Suppl.10 at WK8 and WK16, respectively. At WK24, there was a trend (p = 0.081) for a greater proportion of participants maintaining an s25OHD level ≥50 nmol/L in Gr.Suppl.10 (29/44 = 65.9%) than in Gr.Suppl.5 (21/44 = 47.7%).

Figure 2.

Change (∆) in s25OHD in nanomoles per liter from baseline to weeks 4, 8, 12, and 16 after the onset of the intervention. One hundred thirty-three healthy menopausal women were randomized into 3 groups: Gr.Suppl.0, who were advised not to change their dietary habits; Gr.Suppl.5, who consumed one fortified yogurt providing 5 µg of vitamin D₃ per day; and Gr.Suppl.10, who consumed 2 fortified yogurts providing 10 µg of vitamin D₃ per day. Based on s25OHD values measured in screening samples, the cohort was divided into 2 strata: low, from 25 to 50 nmol/L, and high, from >50 to 75 nmol/L. The statistical significance by repeated measures ANOVA indicates that the differences between Gr.Suppl.5 or Gr.Suppl.10 and Gr.Suppl.0 for the low stratum were significant at p = 0.0012 and p = 0.0001, respectively. For the high stratum, the corresponding significance was p = 0.0020 and p = 0.0001, respectively. The difference between Gr.Suppl.5 and Gr.Suppl.10 was significant in the low stratum (p = 0.0346) but not in the high stratum (p = 0.416). The influence of baseline serum 25OHD level on the progressive increase in serum 25OHD during the intervention was significantly greater in the low stratum than in the high stratum (p = 0.0001).

Figure 3.

Changes in s25OHD during the first 8 weeks following the consumption of 1 or 2 vitamin D₃–fortified yogurts that increased the intake of vitamin D₃ up to 5 and 10 µg per day, respectively. Columns indicate the rate constant of the increase in s25OHD in nanomoles per liter per 1 µg of supplemental vitamin D₃. SD values are written in association with each column. The totality (ALL) of participants (left 2 columns) was separated into a high stratum (middle 2 columns) and low stratum (right 2 columns) according to the values of s25OHD as measured in screening samples: >50 to 75 and 25 to ≤50 nmol/L, respectively. Number of subjects: ALL, 44 and 44 in Gr.Suppl.5 and Gr.Suppl.10, respectively; high stratum, 25 and 28; low stratum, 19 and 16 in Gr.Suppl.5 and Gr.Suppl.10, respectively. Statistical evaluation by ANOVA between Gr.Suppl.5 and Gr.Suppl.10: ALL, p = 0.488; high stratum, p = 0.452; low stratum, p = 0.794. Difference between high stratum and low stratum: p = 0.0006.

Figure 4.

Changes in s25OHD after 8 and 16 weeks of intervention. The 3 randomized groups were divided into 2 subgroups according to enrollment date: early (January 16–18, 2015) and late (March 13–17, 2015). The figure illustrates the interactions between the sampling date (season effect) and the amount of vitamin D₃ (dose effect) as consumed from fortified yogurt that provided daily either 5 µg (Gr.Suppl.5) or 10 µg (Gr.Suppl.10) compared to a time-controlled group (Gr.Suppl.0). The SD values are written in association with each column. See Table 4 for the corresponding absolute values, the number of subjects in each subgroup, as well as the probability level for the differences in s250HD between early and late for Gr.Suppl.0, Gr.Suppl.5, and Gr.Suppl.10.