Vitamin D status in Northern Finland Birth Cohort 1966 and in women with reproductive disorders

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Oulu University Hospital, Lecture Hall 4

Topic of the dissertation

Vitamin D status in Northern Finland Birth Cohort 1966 and in women with reproductive disorders

Doctoral candidate

Medical doctor Johanna Lumme

Faculty and unit

University of Oulu Graduate School, Faculty of Medicine, Pedego Research Unit

Subject of study



Docent Niklas Simberg, Dextra Fertility Clinic


Docent Maarit Niinimäki, Oulu University Hospital, University of Oulu

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Vitamin D status in Northern Finland Birth Cohort 1966 and in women with reproductive disorders

In northern latitudes, the risk of vitamin D deficiency is elevated due to the lack of solar light. To decrease the risk in Finland, a nationwide systematic vitamin D fortification of dairy products and fat spreads has been launched. Vitamin D is essential for bone health. Additional positive health effects of vitamin D have been observed in recent decades. Vitamin D has been suggested to be linked to reproductive disorders in women such as infertility, polycystic ovary syndrome (PCOS) and early-onset menopausal transition.
This thesis included four different studies. The aim was to evaluate vitamin D status in the population living in northern latitudes with an increased risk for vitamin D deficiency and in women with reproductive disorders. The study population included 31- and 46-year-old participants from the prospectively collected large Northern Finland Birth Cohort 1966. The impacts of the vitamin D fortification program were investigated with vitamin D measurements before and after the start of vitamin D fortification in dairy products and fat spreads. Use of vitamin D supplementation was also observed. The aim was to assess whether a history of fertility problems, PCOS or early-onset climacteric phase in women were associated with vitamin D status.
The study results showed that vitamin D status improved, and that the prevalence of vitamin D deficiency decreased after the initiation of the vitamin D fortification program. Seasonal variation in vitamin D concentrations also diminished. Regular vitamin D supplementation and intake of dairy products and fish associated with higher vitamin D status. In women, a history of infertility and decreased fecundability associated with lower vitamin D status. However, based on the results from the present population, PCOS and early-onset climacterium did not seem to increase the risk for vitamin D inadequacy.
In conclusion, the study results support the use of vitamin D fortification and vitamin D supplementation. Achieving adequate vitamin D intake might still need to be ensured. Sufficient vitamin D status should be considered in women with reproductive issues, especially those with infertility problems.
Last updated: 23.1.2024