Progress 12/01/04 to 11/30/06
Outputs
112 women, aged 19 to 35 years, received placebo from March 2005 until September 2005 when they were randomized to receive either placebo or 800 IU vitamin D3 through February 2006. A single dose of vitamin D was used due to the fractionation of the sample by the use of oral contraceptives and unexpectedly high numbers of subjects falling into the 800 IU per day dosage category based on baseline 25(OH)D levels. 98 subjects completed the study in February 2006. Preliminary analysis of the data reveals the results below. In February 2005 the mean (SD) serum 25(OH)D was 61.1 (25.7) nmol/L in all subjects; 47.5 (14.2) nmol/L in the 49 subjects who did not use oral contraceptives (OCP-); and 71.7 (27.7) nmol/L in the 63 subjects who used oral contraceptives (OCP+). There were no significant differences in baseline BMI, body fat, PTH, calcium intake, or vitamin D intake between OCP- and OCP+ groups or between placebo and treatment groups. Serum 25(OH)D levels were
significantly higher (p<.001) in the OCP+ group, but did not differ between placebo and treatment groups. There was a significant inverse correlation between 25(OH)D and PTH levels (r=-.25, p<.01). In September 2005 (n=102), mean 25(OH)D levels were 101.5 (31.8) nmol/L. The levels in OCP- 89.4 (23.1) were significantly lower than OCP+ (111.0 (34.5), p<.0005). The seasonal increase in 25(OH)D levels was not significantly different between OCP+ and OCP- (p<.05). In February 2006 (n=98), after five months of supplementation, the seasonal decrease in 25(OH)D was significantly (p<0.001) less in the treatment group (-6.1 (27.4)) compared to the placebo group (-26.7 (23.1)). In the treatment group, 25(OH)D levels increased by 36.1 (27.2) nmol/L from February 2005 to February 2006 compared to 11.4 (17.3) nmol/L in the placebo group. The seasonal and annual changes in 25(OH)D levels did not differ between OCP- and OCP+. There was a significant inverse correlation between 25(OH)D levels and
body fat and BMI at all time points (r=-.29-.35, p<.01), but there was no correlation between response to supplementation and body fat or BMI. Daily supplementation with 800 IU vitamin D3 during winter maintained optimal 25(OH)D levels (>80 nmol/L) in 73% of subjects, indicating that this dose is too low to meet the needs of the population as a whole. The research did not provide evidence that amount of body fat influences the serum 25(OH)D response to a given oral dose in the practical setting. Data analysis is ongoing.
Impacts
Results from this research will help to determine the appropriate level of vitamin D supplementation needed to achieve optimal serum vitamin D status in winter in northern latitudes. Optimizing serum vitamin D status year-round may help to prevent a number of chronic disease conditions including certain types of cancer, multiple sclerosis, and diabetes.
Publications
- No publications reported this period
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Progress 12/01/04 to 11/30/05
Outputs
Data collection is progressing as scheduled. Baseline serum 25-hydroxyvitamin D [25(OH)D] levels were measured on 112 females between the ages of 19 and 35 years during February 2005. Subjects were then randomized to receive either placebo or 800 IU vitamin D3 per day. Measurement of serum 25(OH)D levels was repeated in September 2005. Currently (January 2006) there are 101 subjects remaining in the study (a 90% retention rate). The final blood samples will be drawn in February 2006. After analyzing the baseline serum 25(OH)D levels, the original plan to customize the level of vitamin D supplementation depending on baseline levels was revised. According to initial serum 25(OH)D levels in February 2005, over half the subjects would have been assigned to receive a dose of 800 IU vitamin D3 per day. Since the numbers of subjects who would have received the other planned doses was too small, the protocol was revised to provide all subjects randomized to the experimental
group with 800 IU vitamin D3 per day. The urinary calcium to creatinine ratio was measured in March and September 2005 and remained within normal limits on all subjects. Other data collection has included two sets of three-day food records and lifestyle questionnaires every three months to document sun exposure behavior, medication and oral contraceptive use, and health changes, among other details. Body composition was measured using dual energy x-ray absorptiometry in March 2005, and measurement will be repeated in March 2006.
Impacts
Results from this research will help to determine the appropriate level of vitamin D supplementation needed to achieve optimal serum vitamin D status in winter at northern latitudes. Optimizing serum vitamin D status year-round may help to prevent a number of chronic disease conditions including certain types of cancer, multiple sclerosis, and diabetes.
Publications
- No publications reported this period
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