Seasonal variation in the serum 25-hydroxyvitamin D levels of young and elderly active and inactive adults in São Paulo, Brazil: The São PAulo Vitamin D Evaluation Study (SPADES)

Abstract

Objective: To evaluate the 25-hydroxyvitamin D [25(OH)D] concentrations in individuals in the city of São Paulo belonging to different age groups and exhibiting specific behavioral characteristics and to correlate the 25(OH)D concentration with the level of UV radiation (UVR).

Patients and methods: A total of 591 individuals were included, distributed as follows: 177 were living in institutions (NURSING, 76.2 ± 9.0 y old), 243 were part of the community elderly (COMMUNITY, 79.6 ± 5.3 y old), 99 were enrolled in a physical activity program targeting the elderly (ACTIVE, 67.6 ± 5.4 y old) and 72 were young (YOUNG, 23.9 ± 2.8 y old). Blood samples from all individuals were collected throughout the year. UVR measurements were taken by an official meteorology institution.

Results: The UVR values varied throughout the year, following a sinusoidal-like pattern. Because of the Earth's orbit, we hypothesized that there would be cyclic patterns for the 25(OH)D and UVR values that repeat every 12 mo. The general formula is represented by the equation P1+P2⋅sin(-2⋅π12⋅(t-P3)) The mean 25(OH)D concentration and the amplitude of the variation were significantly higher for the YOUNG and ACTIVE groups than for the COMMUNITY and NURSING groups. The nadir for UVR was in June, whereas the nadir for the 25(OH)D concentration was in the spring, corresponding to a delay of one season.

Conclusions: There was seasonal variation in the 25(OH)D concentration for all the groups studied; however, the amplitude of the variation was higher for the groups of young and physically active people, possibly due to the higher level of sunlight exposure for these groups. The lowest 25(OH)D concentration was detected in the spring.

Keywords: 25-hydroxyvitamin D; delayed response; nadir; outdoor activity; seasonal variability; sun exposure; ultraviolet radiation.

Figure 1. Distribution of the mean UVR levels (mJ/cm²) according to the month of the year and time of day.

Figure 2. Models representing the sinusoidal curves for each group, which were created from the equation presented in Table 2. The months are represented numerically (1 – January, 2 – February, ….)

Figure 3. Distribution of the mean UVR and 25(OH)D levels for each group according to the month of the year and their respective curves created using sinusoidal equations. Graphical representation of the delay between the lowest UVR level and the lowest 25(OH)D level for the NURSING group.