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Older women do not have seasonal variations of vitamin D levels: a study from a southern country

Abstract:

Objective: The aim was to study whether the seasonal variation of vitamin D [25(OH)-D or calcidiol] is similar or different in younger and older women living in a southern country. Methods: Measurement of serum 25(OH)-D concentration in 739 Chilean women aged 20 to 87 years, residents of Santiago (latitude: 33.48 South) who, during a routine gynaecological checkup, agreed to be evaluated. Results: The mean serum concentration of 25(OH)-D for the group was 24.1 ± 10.5 ng/mL. In women 20 to 39 years, the mean was significantly different from the mean of the ≥60 years old group (25.8 ± 10.6 ng/mL vs 23.9 ± 11.1 ng/mL; P < 0.02). Globally, 38.4% of participants had vitamin D deficiency and 36.1% insufficiency. A deficiency was present in 28.4% of the 20 to 39 years old, and in 43.9% in the ≥60 years old group (P < 0.004). In the whole group, a lower proportion (P < 0.0001) of vitamin D deficiency cases in the youngest women occurred during the summer (23.7%) in comparison to the winter (47.7%). It was observed that the proportion of participants in the 20 to 39 years old group with vitamin D deficiency fell from 48.9% in winter to 4.9% in summer (P = 0.0001). In the older groups, this change (less deficiency) is progressively smaller, 51.2% to 27.6% (P = 0.0020) in women 40 to 59 years old, and it does not happen in women ≥60 years (40% with vitamin D deficiency). Conclusions: Serum vitamin D deficiency [25(OH)-D or calcidiol] is highly prevalent in Santiago, especially in older women (≥60 y) throughout the year. In contrast, in younger women (<40 y), the vitamin D deficiency tends to disappear during summer. More epidemiological studies and targeted prevention actions on vitamin D deficiency are warranted.