Vitamin D 'helps fertility'
A “sunny break may be alternative to IVF,” the Daily Mail has reported. The newspaper said that sunlight can increase levels of vitamin D, which balances sex hormones in women and improves sperm count in men. It added that a study found some couples "may be undergoing unnecessary and costly fertility treatment when spending time in the sun could be the answer".
The news is based on a systematic review of any kind of scientific study that was related to vitamin D and fertility. The review found that there was a lack of human studies, particularly controlled human studies, which had looked at the effect of vitamin D on fertility. This review therefore mostly looked at animal laboratory and observational studies and it is not clear what the implications of this basic research is for infertile couples without further follow up with human studies.
The basic research showed that vitamin D plays a role in biological processes in sperm and ovary cells and may affect levels of sex hormones.
There are many reasons why a couple may be infertile. The cause of a couple’s infertility is usually determined prior to IVF or other fertility treatments. It is not possible to say, as the Daily Mail has suggested, whether spending time in the sun would prevent the need for fertility treatments, without assessing the cause.
Where did the story come from?
The study was carried out by researchers from The Medical University of Graz in Austria and was funded by two Austrian governmental agencies and the Styrian Business Promotion Agency
It was published in the peer-reviewed medical journal the European Journal of Endocrinology.
The Daily Mail accurately reported some of the findings of this review but overemphasised the relevance to infertile couples. Without human controlled trials it is not possible to say whether spending time in the sun could reduce the need for fertility treatments, though the advice does present an attractive option.
What kind of research was this?
This was a systematic review that looked at all of the available scientific papers on vitamin D and fertility. Many factors can cause infertility. The researchers said that in approximately 30 to 40% of infertile couples the underlying cause is problems with the men’s sperm. In women, there are various factors that can mean that they do not release an egg or make it difficult for a fertilised egg to attach to and grow in the uterus. The researchers say that one major cause of female infertility is polycystic ovary syndrome (PCOS), a condition that affects their sex hormones.
This systematic review took a broad sweep approach to look at the evidence for a link between vitamin D and any aspect of fertility. Although systematic reviews are a good way of comprehensively looking at all of the evidence in an area, there can sometimes be limitations to pooling data if the included studies differ in design. In this systematic review, the researchers included both human and animal studies and care has to be taken in reporting which of the included studies have relevance to humans.
What did the research involve?
The researchers looked in one medical database for English language publications up to October 2011. They searched the terms and phrases: vitamin D, fertility, vitamin D and reproduction, vitamin D and PCOS. They also searched for alternative names for vitamin D and looked at the reference lists from the studies their search had found.
In most systematic reviews, the researchers listed their criteria for including or excluding studies. They may, for example, only include some study designs and not others. However, in this review, the researchers did not say how they decided to include studies. The researchers said that they did not find many human studies and have included animal and laboratory studies that can give information about the basic biology of vitamin D but do not tell us whether vitamin D can help infertile couples.
What were the basic results?
The researchers said studies have shown that:
- The vitamin D receptor has been found in human testes and sperm in men, and in the ovaries and placenta in women.
- Removing the vitamin D receptor in genetically modified mice leads to decreased sperm count and motility and affects the structure of the testes. In female genetically modified mice, removing this receptor causes changes to the structure of the ovaries and uterus.
- One study reported that in high latitude countries there is a large difference in the amount sunlight in the summer and winter. Also there are decreased conception rates in the winter months and peak conception rates in the summer months.
- One study suggested that women’s ovulation rates and the receptiveness of their uterus for a fertilised egg is reduced during long dark winters in high latitude countries.
- Studies investigating the association of vitamin D status with IVF had inconsistent results. One study found no association; one found that higher vitamin D levels had a positive effect, and one found that women with sufficient vitamin D had poorer outcomes then women with insufficient vitamin D.
- Three studies found a correlation between low vitamin D and some, but not all of the symptoms of PCOS.
- Studies looking at the effects of vitamin D on fertility in healthy women are sparse. One study of 101 young women found that higher vitamin D levels were associated with lower sex hormone levels. A small study found that a course of vitamin D supplementation had no statistically significant effect on sex hormone levels.
- One study of 300 men found that there was an association between higher vitamin D levels and higher sperm motility, but another study found no association between vitamin D and sperm count and the proportions of normal sperm.
- One study of 2299 men found an association between vitamin D levels and male sex hormone levels.
How did the researchers interpret the results?
The researchers said that evidence based largely on animal work and observation studies rather than controlled trials has suggested that vitamin D deficiency might be important for hormone disturbances including fertility in women as well as men. They say that these findings deserve further investigation.
This systematic review looked for all available studies prior to October 2011 that had looked at fertility and vitamin D. Besides this very broad search the review included animal, laboratory and observational studies, which means that it is difficult to draw conclusions on the implications of this data for people. The researchers noted that there was a real lack of human controlled studies. As a result, it is not possible to say that fertility problems in men and women could be helped by vitamin D supplementation, increasing vitamin D through diet or spending time in the sun.
Vitamin D and its human effects is currently a topic of immense interest to the public and to policy makers. This research looked at another angle, that of fertility, and is useful in giving a broad overview of the basic biology of vitamin D and a range of biological processes involved in infertility. It highlighted where there has been a lack of studies and where more work could be done. Future assessments into the role of vitamin D in fertility should as a minimum involve controlled human trials.
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