[Ultraviolet radiation impact on seasonal variations of serum 25-hydroxy-vitamin D in healthy young adults in Buenos Aires]. / Variaciones estacionales de 25 (OH) vitamina D en jóvenes sanos y su asociación con la radiación ultravioleta en Buenos Aires.

Exposure to sunlight (ES) is the main source of vitamin D. There are few reports regarding the seasonal variations of serum 25(OH) vitamin D in young adults and its correlation with ultraviolet radiation dose (UVRd). Our aims were to determine 25OHD variations in young adults and assess the correlation between 25OHD levels, dietary calcium intake (DCI) and the UVRd. Eighty two healthy volunteers were prospectively studied: 42 women and 40 men. Serum 25OHD, calcium, phosphorus and magnesium were measured at the end of winter and at the end of summer. ES and UVRd were determined hourly in winter and summer. Seasonal variation in serum 25OHD levels was observed with significantly higher levels in summer in both gender. Serum 25OHD <20 ng/ml was more frequently found in winter (42.6% in women and 50% in men). The ES and UVRd were significantly lower in winter vs. summer. ES and UVRd positively correlated with 25OHD only in winter in both men and women. DCI was lower than recommended and did not correlate with 25OHD levels.

Variaciones estacionales de 25 (OH) vitamina D en jóvenes sanos y su asociación con la radiación ultravioleta en Buenos Aires / Ultraviolet radiation impact on seasonal variations of serum 25-hydroxyvitamin D in healthy young adults in Buenos Aires

El estatus de vitamina D depende principalmente de la exposición solar (ES). Son escasos los informes de las variaciones estacionales de 25(OH)vitamina D, 25OHD, en adultos jóvenes y su relación con la dosis de radiación solar ultravioleta (dRUV). El objetivo de este trabajo fue medir variaciones estacionales de 25OHD en adultos jóvenes estableciendo la correlación con la ingesta dietaria de calcio (IDCa) y la dRUV. Se realizó un estudio prospectivo en individuos sanos: 42 mujeres y 40 varones. Se dosaron a fin de invierno y fin de verano: 25OHD, calcio, fósforo y magnesio. Se evaluó ES y dRUV para cada hora del día en invierno y verano. Se observó una variación estacional de 25OHD con valores significativamente mayores en verano tanto en varones como en mujeres. El 42.6% de las mujeres y el 50.0% de los varones tenían 25OHD <20 ng/ml en invierno. La ES y la dRUV fueron significativamente inferiores en invierno que en verano. Sólo en invierno se halló una correlación positiva entre ES y dRUV con 25OHD en ambos sexos. La IDCa fue insuficiente y no correlacionó con 25OHD.

Exposure to sunlight (ES) is the main source of vitamin D. There are few reports regarding the seasonal variations of serum 25(OH) vitamin D in young adults and its correlation with ultraviolet radiation dose (UVRd). Our aims were to determine 25OHD variations in young adults and assess the correlation between 25OHD levels, dietary calcium intake (DCI) and the UVRd. Eighty two healthy volunteers were prospectively studied: 42 women and 40 men. Serum 25OHD, calcium, phosphorus and magnesium were measured at the end of winter and at the end of summer. ES and UVRd were determined hourly in winter and summer. Seasonal variation in serum 25OHD levels was observed with significantly higher levels in summer in both gender. Serum 25OHD <20 ng/ml was more frequently found in winter (42.6% in women and 50% in men). The ES and UVRd were significantly lower in winter vs. summer. ES and UVRd positively correlated with 25OHD only in winter in both men and women. DCI was lower than recommended and did not correlate with 25OHD levels.

The relationship of preconception thyrotropin levels to requirements for increasing the levothyroxine dose during pregnancy in women with primary hypothyroidism.

BACKGROUND: Most women with hypothyroidism require an increase in their dose of levothyroxine (LT4) after conception. To minimize fetal and maternal complications of maternal hypothyroidism, it is thought that women should be rapidly restored to the euthyroid state. The objectives of this study was to determine the percentage of hypothyroid women who would need to increase their dose of LT4 dose even if they had a preconception (pre-C) serum thyrotropin (TSH) of <2.5 mIU/L as recommended by the Endocrine Society's guidelines and to ascertain whether there was a relationship between the pre-C TSH value and the need to increase the LT4 dose during pregnancy. METHODS: Fifty-three pregnant women with hypothyroidism on LT4 treatment in whom the pre-C serum TSH was <2.5 mIU/L, but which was within the normal range, within the 6 months before pregnancy were retrospectively studied. An additional selection criterion was that their LT4 dose at the time of their first prenatal visit was the same as that received pre-C. RESULTS: Seventeen patients had to increase their LT4 dose during pregnancy, because their serum TSH was increased at the time of the first prenatal visit (Group 1); and 36 patients did not have to increase their dose of LT4 during pregnancy (Group 2). The pre-C TSH was significantly higher in Group 1 (1.55 ± 0.62 mIU/L) than in Group 2 (0.98 ± 0.67 mIU/L). When pre-C TSH range was 1.2-2.4 mIU/L, 50% of the patients required an increase in the LT4 dose during pregnancy. In contrast, when the pre-C TSH was <1.2 mIU/L, only 17.2% (p< 0.02) had to increase the LT4 dose during pregnancy. CONCLUSIONS: We suggest that in women with hypothyroidism who are planning to become pregnant, serum TSH levels should be in the normal range but should not be greater than about 1.2 mIU/mL.