A new trial published in Reproductive Endocrinology has found that in polycystic ovary syndrome, vitamin D may have a minimal effect on insulin resistance and blood pressure, however further research is warranted.
Polycystic ovary syndrome (PCOS) is a complex condition that affects approximately 5% of women. The principal features of PCOS are lack of ovulation resulting in irregular periods, few or no periods, infertility, and ovaries with multiple cysts.
For reasons still not fully understood, insulin resistance is common in women with PCOS. Insulin resistance is a condition in which cells fail to respond to the action of the hormone insulin. This causes increased insulin production and leads to unhealthily high blood sugar and insulin levels.
Furthermore, higher levels of insulin in the blood can lead to overproduction of testosterone, which is common in PCOS. A high amount of testosterone in women can lead to the development of too many follicles in the ovary, contributing to infertility.
There’s a well-established link between vitamin D and insulin. Researchers are finding in randomized controlled trials that higher vitamin D intake may improve insulin sensitivity and resistance.
However, in PCOS, research looking at vitamin D’s role in insulin sensitivity has been limited and inconsistent. The few trials looking at this relationship used low vitamin D doses and found insignificant results. If vitamin D could help with insulin sensitivity in PCOS, it would tremendously help with some aspects of the condition.
Recently, researchers at the Pennsylvania State University College of Medicine conducted a randomized controlled trial on the effects of high-dose vitamin D supplementation on insulin sensitivity in women with PCOS.
The researchers recruited 28 mainly obese women with PCOS between the ages of 18 and 45 years. These women were randomized into two groups. Thirteen received 12,000 IU/day of vitamin D3 and 15 received a placebo per day for 12 weeks. The researchers checked calcium levels at 4 and 8 weeks and at the end of the trial to ensure that no participants developed hypercalcemia.
At baseline and at the end of the study, the researchers measured vitamin D levels and markers of insulin sensitivity using the quantitative insulin sensitivity check index (QUICKI). QUICKI is measured using an equation that determines insulin sensitivity by computing both fasting insulin and fasting glucose levels. A low QUICKI value indicates more insulin resistance.
Did a very high-dose of vitamin D supplementation raise QUICKI values and improve insulin sensitivity?
After 12 weeks, 4 women from the placebo group dropped out, while 2 from the vitamin D group dropped out. The researchers did an intention-to-treat analysis, meaning that despite these dropouts, the researchers still included the dropouts in their analysis of the effectiveness of vitamin D vs. placebo.
After 12 weeks, here is what the researchers found:
- There was no significant difference in QUICKI scores between the two groups.
- In the vitamin D3 group, there was a non-significant reduction in 2-hour insulin levels, although this approached significance (p=.05).
- In the vitamin D3 group, there was a trend toward a reduction in 2-hour glucose.
- The placebo group experienced a significant increase in diastolic blood pressure, leading the researchers to speculate that vitamin D3 may have a protective effect on blood pressure.
The researchers concluded,
“High-dose vitamin D significantly increased 25(OH)D levels and had a protective effect on blood pressure in women with PCOS. Insulin sensitivity, both with homeostatic and integrated measures, was unchanged despite the trend toward decreased 2-hour insulin.”
The researchers didn’t note any limitations to the study. However, the study only looked at 28 women, meaning we cannot say for sure if these results would apply to larger populations. Furthermore, 6 women dropped out during their trial, which could have impacted their results.
Another issue is that all of the women in the vitamin D group were obese, while just 87% of the women in the placebo group were obese, so it is hard to know if this affected the results of the study. We also don’t know if vitamin D supplementation would have different affects on non-obese women.
Finally, the trial only lasted 12 weeks, so we don’t know if these findings apply for longer periods of supplementation. It could be the case that longer periods of vitamin D supplementation have benefit, while shorter periods don’t.
The results of this trial suggest that vitamin D supplementation of 12,000 IU/day has minimal effect on insulin sensitivity in women with PCOS. This does not mean that vitamin D provides no benefit for women with PCOS. In fact, a randomized controlled trial published in late 2013 found that high-dose vitamin D supplementation may help increase the probability of becoming pregnant in women with PCOS. Furthermore, they found a protective effect on blood pressure in this present trial.
This present study found trends toward vitamin D helping with insulin sensitivity. A larger and longer trial may have shown significant effects. We need larger randomized controlled trials in this area to fully understand the relationship between PCOS and vitamin D.