Vitamin D (25OHD) Serum Seasonality in the United States

Background

Vitamin D is an important micronutrient for health. Hypovitaminosis D is thought to play a role in the seasonality of a number of diseases and adverse health conditions. To refine hypotheses about the links between vitamin D and seasonal diseases, good estimates of the cyclicality of serum vitamin D are necessary.

Objectives

The objective of this study is to describe quantitatively the cyclicality of 25-hydroxyvitamin D (25OHD) in the United States. We provide a statistical analysis with weekly time resolution, in comparison to the quarterly (winter/spring/summer/fall) estimates already in the literature.

Methods

We analyzed time series data on 25OHD, spanning 287 consecutive weeks. The pooled data set comes from 3.44 million serum samples from the United States. We statistically analyzed the proportion of sera that were vitamin D sufficient, defined as 25OHD ng/mL, as a function of date.

Results

In the United States, serum 25OHD follows a lagged pattern relative to the astronomical seasons, peaking in late summer (August) and troughing in late winter (February). Airmass, which is a function of solar altitude, fits the 25OHD data very well when lagged by 8 weeks.

Conclusions

Serum vitamin D levels can be modeled as a function of date, working through a double-log transformation of minimal solar airmass (easily calculated from solar altitude, retrievable from an online solar altitude/azimuth table).     

Temporal Relationship between Vitamin D Status and Parathyroid Hormone in the United States

Background

Interpretation of parathyroid hormone (iPTH) requires knowledge of vitamin D status that is influenced by season.

Objective

Characterize the temporal relationship between 25-hydroxyvitamin D₃ levels [25(OH)D₃] and intact iPTH for several seasons, by gender and latitude in the U.S. and relate 25-hydrovitamin D₂ [25(OH)D₂] levels with PTH levels and total 25(OH)D levels.

Method

We retrospectively determined population weekly-mean concentrations of unpaired [25(OH)D₂ and 25(OH)D₃] and iPTH using 3.8 million laboratory results of adults. The 25(OH)D₃ and iPTH distributions were normalized and the means fit with a sinusoidal function for both gender and latitudes: North >40, Central 32–40 and South <32 degrees. We analyzed PTH and total 25(OH)D separately in samples with detectable 25(OH)D₂ (≥4 ng/mL).

Findings

Seasonal variation was observed for all genders and latitudes. 25(OH)D₃ peaks occurred in September and troughs in March. iPTH levels showed an inverted pattern of peaks and troughs relative to 25(OH)D₃, with a delay of 4 weeks. Vitamin D deficiency and insufficiency was common (33% <20 ng/mL; 60% <30 ng/mL) as was elevated iPTH levels (33%>65 pg/mL). The percentage of patients deficient in 25(OH)D₃ seasonally varied from 21% to 48% and the percentage with elevated iPTH reciprocally varied from 28% to 38%. Patients with detectable 25(OH)D₂ had higher PTH levels and 57% of the samples with a total 25(OH)D > 50 ng/mL had detectable 25(OH)D₂.

Interpretation

25(OH)D₃ and iPTH levels vary in a sinusoidal pattern throughout the year, even in vitamin D₂ treated patients; 25(OH)D₃, being higher in the summer and lower in the winter months, with iPTH showing the reverse pattern. A large percentage of the tested population showed vitamin D deficiency and secondary hyperparathyroidism. These observations held across three latitudinal regions, both genders, multiple-years, and in the presence or absence of detectable 25(OH)D₂, and thus are applicable for patient care.     

Vitamin D effective ultraviolet wavelengths due to scattering in shade

Solar UVB radiation (280–320 nm) is an initiator of Vitamin D₃ production in the human skin. While numerous studies have been conducted in relation to the biological impact of UV exposure in full sun, less research has investigated the irradiances in shade. The purpose of this study was to determine the levels of UV radiation in relation to Vitamin D₃ induction with six commonly encountered shade environments for the larger solar zenith angles observed during autumn and winter. Spectral UV irradiance measurements were made under relatively clear sky conditions at a sub-tropical Southern Hemisphere site for six specific shade environments and solar zenith angle between 35° and 60° to investigate the biologically effective UV irradiances for pre-Vitamin D₃ production. Data from this research indicates that pre-Vitamin D₃ effective UV wavelengths in the shade were most significant for tree shade and a shade umbrella. Compared to that in full sun, pre-Vitamin D₃ effective UV wavelengths were at levels of approximately 52 and 55%, respectively, beneath the shade umbrella and in tree shade. UVB irradiance levels in the shade of a northern facing covered veranda and in a car with windows closed were significantly less than those beneath the shade umbrella, with levels of approximately 11 and 0%, respectively, of those in full sun. Shade is important as a UV minimisation strategy; however, it may also play an important role in providing the human body with adequate levels of UVB radiation for pre-Vitamin D₃ production without experiencing the relatively higher levels of UVA irradiances present in full sun.     

The penetration of ultraviolet radiation to the ground

The evolution of analytic formulas for characterizing the ultraviolet spectral ir-radiance penetrating to the ground is briefly described. Analytic spectral functions for the extraterrestrial solar spectral irradiance, the ozone absorption coefficient, Rayleigh scattering coefficients and aerosol scattering and absorption coefficients, which are used as basic inputs, are given. With Beer's law, these give immediately the direct solar spectral irradiance. A ratio technique described in quantitative detail gives a procedure for calculating the skylight component of the UV radiation reaching the ground. The influence of ground reflectivity, clouds and a possible connection between photobiology and radiological physics are discussed. Finally the advantages of multiwavelength monitoring are described, using monochromators similar to those used in satellite ozone sounding to serve the needs of the photobiology and the atmospheric science communities.     

Photoisomerization of provitamins D under influence of various ultraviolet radiation]

The influence of various sources of ultraviolet radiation on the photoisomerization of provitamins D--ergosterol and 7-dehydrocholesterol--was studied under industry-like conditions. The yield of previtamins and, consequently, vitamins D was higher with the use of erythemic lamps with luminophore E-2 and luminophore E-3 than with the use of lamps PRK-2.     

The castor-oil plant in the United States

About 125,000,000 pounds of castor oil are annually used in the United States in the manufacture of paints and varnishes, fatty acids, sulphonated oils, soap and other important products, 95% of which is imported either as seed or expressed oil. Attempts are now being made to revive a former American industry in the growing of domestic crops.     

The evolution-creation controversy in the United States

The evolution-creation controversy in the United States has waxed and waned over the last hundred years. The history of this controversy is traced in general terms from the early Fundamentalist Movement at the close of the nineteenth century to the present time. Of special note are summaries of the more well-known court cases including the so-called Scopes Monkey Trial of the mid-1920s and the more recent Epperson vs. Arkansas decision of 1968.