Researchers studied 148 adults with type 2 diabetes to understand how vitamin D levels affect blood sugar control and heart health. They found that people with low vitamin D had higher blood sugar levels, higher cholesterol, and more protein in their urine (a sign of kidney stress). The study suggests that vitamin D may play an important role in how our bodies manage blood sugar and protect our kidneys. While this doesn’t prove vitamin D deficiency causes these problems, it shows a strong connection worth investigating further.

The Quick Take

  • What they studied: Whether people with type 2 diabetes who have low vitamin D levels also have worse blood sugar control, higher cholesterol, and kidney problems compared to those with normal vitamin D levels.
  • Who participated: 148 adults with type 2 diabetes (average age 57 years, about half men and half women) visiting a family medicine clinic in Turkey between July and December 2019.
  • Key finding: Adults with low vitamin D (below 20 ng/mL) had significantly higher blood sugar levels, total cholesterol, and protein in their urine compared to those with adequate vitamin D levels.
  • What it means for you: If you have type 2 diabetes, checking your vitamin D levels may be worth discussing with your doctor. Low vitamin D appears connected to harder-to-control blood sugar and higher cholesterol, though more research is needed to confirm whether fixing low vitamin D actually improves these conditions.

The Research Details

This was a retrospective study, meaning researchers looked back at patient records from a clinic in Istanbul, Turkey. They collected information from 148 adults with type 2 diabetes who visited between July and December 2019. The researchers divided patients into two groups based on their vitamin D levels: those with low vitamin D (below 20 ng/mL) and those with adequate levels (20 ng/mL or higher). They then compared blood sugar control, cholesterol levels, and kidney function markers between the two groups using statistical analysis.

The researchers measured several important health markers: vitamin D levels in the blood, glycated hemoglobin (a measure of average blood sugar over 3 months), total cholesterol and LDL cholesterol (bad cholesterol), and microalbumin/creatinine ratio (a sign of kidney stress). They used standard medical tests and statistical software to analyze whether differences between groups were meaningful.

This approach is useful because it examines real patient data from actual medical practice rather than controlled laboratory conditions. By comparing patients with different vitamin D levels, researchers can identify patterns and associations. However, because this is a retrospective study looking at past records, it can show relationships but cannot prove that low vitamin D directly causes the problems observed.

Strengths: The study included a reasonable number of participants (148) and measured multiple important health markers. The researchers used proper statistical methods to determine if differences were meaningful. Limitations: This was a single-center study from one clinic in Turkey, so results may not apply to all populations. The study design cannot prove cause-and-effect relationships. The researchers didn’t account for other factors that might affect vitamin D levels or blood sugar control, such as sun exposure, diet, or medication use.

What the Results Show

The study found clear differences between the low vitamin D group and the adequate vitamin D group. Adults with low vitamin D had significantly higher glycated hemoglobin levels (7.8% vs 7.3%), meaning their blood sugar was harder to control. They also had higher total cholesterol and LDL cholesterol (bad cholesterol), suggesting worse lipid profiles. Additionally, people with low vitamin D had higher levels of protein in their urine, which indicates potential kidney stress.

When researchers looked at the relationship between vitamin D and other measurements, they found that lower vitamin D levels were associated with higher blood sugar levels and higher total cholesterol. These associations were statistically significant, meaning they were unlikely to occur by chance alone.

The average vitamin D level across all participants was 22.81 ng/mL, which is considered low. About half the patients (76 out of 148) had vitamin D levels below 20 ng/mL, while the other half had adequate levels.

The study also noted that lymphocyte counts (a type of white blood cell) were higher in the low vitamin D group, suggesting possible inflammation. This is interesting because inflammation is thought to play a role in both diabetes complications and vitamin D deficiency. The findings suggest vitamin D may influence how the body manages inflammation, which could affect blood sugar control and kidney function.

These findings align with previous research suggesting vitamin D plays a role in blood sugar metabolism and kidney health. Other studies have shown connections between low vitamin D and poor diabetes control, though results have been mixed. This study adds to the evidence that vitamin D deficiency may be associated with worse diabetes outcomes, but it doesn’t change current medical practice since more definitive research is still needed.

This study has several important limitations. First, it only looked at data from one clinic in Turkey, so results may not apply to other populations or countries. Second, the study design cannot prove that low vitamin D causes these problems—only that they occur together. Third, researchers didn’t measure or account for other important factors like how much sun exposure patients got, their diet, medications they were taking, or their exercise levels. Fourth, the study was relatively small (148 patients) and conducted several years ago. Finally, the researchers didn’t follow patients over time, so we don’t know if treating vitamin D deficiency would actually improve blood sugar control or kidney function.

The Bottom Line

If you have type 2 diabetes, discuss vitamin D testing with your doctor (moderate confidence). If testing shows low vitamin D, your doctor may recommend supplementation, though current evidence doesn’t definitively prove this will improve blood sugar control (low to moderate confidence). Don’t change your diabetes medications or treatment based on this study alone. Continue following your doctor’s diabetes management plan while addressing vitamin D status as part of overall health.

Adults with type 2 diabetes should be aware of this research, especially if they have difficulty controlling their blood sugar or live in areas with limited sun exposure. People with risk factors for vitamin D deficiency (limited sun exposure, darker skin in northern climates, dietary restrictions) may want to discuss vitamin D testing with their doctor. This research is less relevant for people without diabetes, though vitamin D is important for everyone’s health.

If vitamin D deficiency is corrected through supplementation, improvements in blood sugar control might take several weeks to months to appear, similar to other diabetes management changes. However, this study doesn’t prove that correcting vitamin D will improve these markers. Any changes should be monitored by your healthcare provider through regular blood tests.

Want to Apply This Research?

  • Track your vitamin D supplementation (if recommended by your doctor) and record your blood sugar readings daily. Note any changes in average blood sugar levels over 4-week periods to see if vitamin D supplementation correlates with better control.
  • If your doctor recommends vitamin D supplementation, set a daily reminder to take it at the same time each day. Log the dose and time in your app. Also track sun exposure time (15-30 minutes daily when possible) as a natural source of vitamin D, noting weather and season.
  • Create a monthly summary view comparing your average blood sugar levels, cholesterol readings (from lab work), and vitamin D supplementation consistency. Share this data with your doctor during regular check-ups to assess whether vitamin D management is contributing to better overall diabetes control.

This research shows an association between low vitamin D and worse diabetes control, but does not prove that vitamin D deficiency causes these problems. This information is for educational purposes only and should not replace medical advice from your healthcare provider. Do not start, stop, or change any diabetes medications or treatments based on this study. If you have type 2 diabetes, consult with your doctor before taking vitamin D supplements or making changes to your diabetes management plan. Your doctor can determine if vitamin D testing and supplementation are appropriate for your individual situation.