Vitamin D status and its adequacy in healthy Danish perimenopausal women: relationships to dietary intake, sun exposure and serum parathyroid hormone

Abstract

We conducted this study to assess the prevalence of vitamin D insufficiency in a population of normal perimenopausal women, to examine the influence of sun exposure and vitamin D intake on the concentration of 25-hydroxyvitamin D (25OHD) and to examine the association between parathyroid hormone (PTH) and 25OHD. A total of 2016 healthy women aged 45±58, who had recently undergone a natural menopause, were enrolled over a 2´5-year period in the Danish Osteoporosis Prevention Study. A marked seasonal fluctuation of 25OHD was seen, with an abrupt rise in June and high values until October. The fluctuation could be related to number of hours of sunshine per month with a two months time lag. Dietary vitamin D intake, vitamin supplementation, sunlight exposure, and use of sun-bed were all significantly related to 25OHD concentrations. Sun exposure seemed to contribute the most. The overall prevalence of vitamin D deficiency (defined as serum 25OHD , 25 nmolal) was 7 %. However, in the subgroup avoiding direct sunshine and abstaining from vitamin D supplementation 32´8 % were vitamin D deficient in the winter±spring period. Although mean PTH was increased in the group with low serum 25OHD, PTH was not a sensitive marker of hypovitaminosis D in the individual, as only 16 % of those with vitamin D deficiency had PTH levels above normal range. Thus, we have shown, that healthy middle-aged Danish women are prone to vitamin D insufficiency in the winter±spring period, if they avoid sun exposure in the summer period and abstain from vitamin D supplementation.

Postpartum vitamin D insufficiency and secondary hyperparathyroidism in healthy Danish women

“…Our strict inclusion and exclusion criteria and the magnitude of study program may result in a preferential selection of the healthy, socially and financially more competent participants who are less likely to have vitamin D deficiency. The long duration of breastfeeding in our study compared with other studies (Arbejdsgruppe under Fagligt Forum for Amtssundhedsplejersker, 2003) and the low prevalence of smoking (Hegaard et al, 2004), which decrease plasma 25-OHD (Brot et al, 2001), support this concept. Hence, we feel it unlikely that we have selected participants more prone to be vitamin D insufficient or deficient than the background population of lactating Danish women in general.…”

“…This secondary hyperparathyroidism is parallel to observations in several non-postpartum populations (DawsonHughes et al, 1991;Brot et al, 2001;Lips, 2001;Jesudason et al, 2002;Vieth et al, 2003;Mosekilde, 2005). The increased plasma levels of PTH affect calcium homeostasis probably by increasing renal calcium reabsorption and enhancing renal 1.25(OH) 2 D synthesis.…”

“…The corresponding figures during summer were 58.9 and 3%, respectively. The study also revealed a connection between inadequate sun exposure and vitamin D deficiency and documented the effect of vitamin D supplementation on P-25OHD (Brot et al, 2001).…”

“…In this population, vitamin D deficiency was found in 42% during winter and in 4% during summer . Moreover, a study in 2000 perimenopausal women disclosed that 23% were vitamin D insufficient and 7% deficient during winter (Brot et al, 2001). The corresponding figures during summer were 58.9 and 3%, respectively.…”

“…At higher latitudes, cutaneous vitamin D production varies with season because of the reduced UVB exposure during winter (Holick, 1999;Brot et al, 2001;Mosekilde, 2005). Usually, vitamin D status is assessed by measuring plasma 25-hydroxyvitamin D (P-25OHD) (Lips, 2001;Mosekilde, 2005).…”