Research shows that kidney damage and eye damage from diabetes are the strongest predictors of serious foot complications like ulcers and amputations. According to Gram Research analysis of 21 major studies, nerve damage, high blood sugar levels, vitamin D deficiency, male sex, older age, and smoking also significantly increase risk. These factors work together through multiple pathways involving blood vessel damage, metabolic stress, and self-care behaviors, suggesting that effective prevention requires addressing multiple risk factors simultaneously.
A comprehensive analysis of 21 major research studies has identified the key factors that put people with diabetes at risk for serious foot complications like ulcers and amputations. According to Gram Research analysis, kidney damage and eye problems from diabetes are the strongest predictors, while nerve damage, high blood sugar levels, vitamin D deficiency, and smoking also significantly increase risk. The research reveals that foot complications develop through multiple interconnected pathways involving blood vessel damage, metabolic stress, foot vulnerability, and how well people follow their care plans. Understanding these risk factors could help doctors identify patients who need extra foot care and prevention strategies.
Key Statistics
A 2026 umbrella review analyzing 21 systematic reviews found that diabetic kidney damage and eye damage showed the strongest evidence (Class I) for predicting foot complications in people with diabetes.
According to a 2026 analysis of 32 risk factors across 21 research reviews, diabetic nerve damage, male sex, high HbA1c levels, vitamin D deficiency below 50 nmol/L, older age, and longer diabetes duration all had strong evidence (Class II) linking them to foot ulcers or amputations.
A 2026 research synthesis found that smoking and poor medication adherence were specifically associated with amputation risk, while most other factors primarily predicted foot ulcers, suggesting a progression pathway from ulcers to more severe outcomes.
The 2026 umbrella review identified that foot complications develop through four interconnected pathways: systemic blood vessel damage, poor blood sugar control, local foot vulnerability from nerve damage, and care-related behaviors like smoking and medication adherence.
The Quick Take
- What they studied: What factors and conditions make people with diabetes more likely to develop serious foot problems, including foot ulcers (open sores) and amputations (surgical removal of toes, feet, or legs)?
- Who participated: Researchers analyzed 21 previously published systematic reviews and meta-analyses that collectively examined dozens of studies involving thousands of people with diabetes across multiple countries.
- Key finding: Kidney damage and eye damage from diabetes are the strongest predictors of foot complications, with very strong scientific evidence. Nerve damage, male sex, high blood sugar levels, vitamin D deficiency, older age, and longer time living with diabetes also significantly increase risk.
- What it means for you: If you have diabetes, knowing these risk factors can help you work with your doctor to get preventive care. Regular foot checks, blood sugar management, vitamin D screening, and smoking cessation are particularly important if you have any of these risk factors.
The Research Details
This was an umbrella review, which means researchers looked at 21 existing systematic reviews and meta-analyses (the highest-quality types of research summaries) published between the start of medical literature records through March 2025. They searched nine major medical databases in English and Chinese to find all relevant studies. The researchers examined 32 different factors that might be associated with foot complications in people with diabetes, organizing them into five categories: demographic factors (age, sex), physical characteristics (blood sugar control, vitamin levels), foot-specific issues (nerve damage, foot structure), psychological factors (depression, anxiety), and behavioral factors (smoking, medication adherence).
To ensure quality, the researchers used a standardized tool called AMSTAR 2 to evaluate how well each of the 21 reviews was conducted. They also checked for overlap between reviews to avoid counting the same evidence multiple times. When appropriate, they performed a second-order meta-analysis, which means they combined results from multiple reviews to get stronger conclusions.
The entire project was registered in advance on PROSPERO (an international database for systematic reviews) to ensure transparency and prevent bias in how they reported their findings.
This approach is important because evidence about diabetes foot complications is scattered across hundreds of individual studies and dozens of review articles. By synthesizing all this evidence together and grading its quality, researchers can identify which risk factors have the strongest scientific support and which ones need more research. This helps doctors prioritize which patients need the most intensive prevention strategies.
This is a high-quality research synthesis because it: (1) searched multiple databases in two languages to find all relevant studies, (2) used a validated tool to assess the quality of included reviews, (3) was registered in advance to prevent selective reporting, (4) graded the strength of evidence for each finding, and (5) examined overlap between reviews to avoid double-counting evidence. The main limitation is that the quality of conclusions depends on the quality of the 21 reviews included, and some individual studies within those reviews may have had methodological weaknesses.
What the Results Show
The research identified two factors with the strongest possible evidence (Class I evidence): diabetic nephropathy (kidney damage) and diabetic retinopathy (eye damage). These conditions indicate that diabetes has already caused significant damage to small blood vessels throughout the body, which also affects the feet.
Seven additional factors had strong evidence (Class II evidence) supporting their association with foot complications: diabetic peripheral neuropathy (nerve damage in the feet and legs), male sex, higher HbA1c levels (a measure of long-term blood sugar control), vitamin D deficiency (levels below 50 nmol/L), older age, and longer duration of diabetes. These factors work together to increase vulnerability to foot problems.
The research found that most identified risk factors were associated with diabetic foot ulcers (open sores on the feet). However, smoking and poor adherence to outpatient care were specifically linked to amputation risk, suggesting these behavioral factors may push complications from ulcers to more severe outcomes. Male sex was associated with both ulcers and amputations.
The overall pattern suggests that foot complications develop through multiple interconnected pathways: systemic microvascular burden (widespread small blood vessel damage), metabolic exposure (poor blood sugar control), local foot vulnerability (nerve damage and structural problems), and care-related behaviors (smoking, medication adherence, foot care practices).
The research identified several other factors with moderate evidence, though these were less consistently supported across studies. These included psychological factors like depression and anxiety, which may affect self-care behaviors. The review also noted that the specific type and severity of diabetes complications often cluster together—people with kidney damage often also have eye damage and nerve damage, suggesting a common underlying mechanism of blood vessel injury.
This umbrella review synthesizes and updates previous knowledge by bringing together evidence from 21 major reviews published over many years. It confirms that microvascular complications (kidney and eye damage) are indeed the strongest predictors, which aligns with clinical understanding that these conditions indicate systemic vascular damage. The strong evidence for nerve damage as a risk factor is consistent with previous research showing that loss of protective sensation in the feet makes ulcers more likely. The emphasis on behavioral factors like smoking and medication adherence adds important context that foot complications are not purely biological—they also depend on modifiable lifestyle and care factors.
The review’s conclusions are limited by the quality of the 21 included reviews, which may have had varying methodological rigor. Some risk factors were studied more extensively than others, so the absence of strong evidence for a particular factor doesn’t necessarily mean it’s unimportant—it may just mean fewer high-quality studies have examined it. The review primarily included published studies, which may miss important negative findings that weren’t published. Additionally, most included studies were observational rather than experimental, so while associations were identified, cause-and-effect relationships cannot be definitively established. The review also noted that some factors may be markers of disease severity rather than independent risk factors.
The Bottom Line
High confidence: If you have diabetes, work with your healthcare provider to maintain good blood sugar control (target HbA1c levels), get regular eye and kidney function screening, and have your feet examined regularly by a healthcare professional. If you have nerve damage in your feet, extra vigilance is needed. Moderate confidence: Maintain adequate vitamin D levels through diet, supplementation, or sun exposure as recommended by your doctor. Stop smoking if applicable, as it significantly increases amputation risk. Ensure you take all prescribed medications and attend all recommended appointments. Low to moderate confidence: Address depression or anxiety if present, as these may affect self-care behaviors.
These findings are most relevant for people with type 1 or type 2 diabetes, especially those with existing complications like kidney or eye damage. Healthcare providers should use this information to identify high-risk patients who need intensive foot care education and monitoring. People with diabetes who have multiple risk factors (older age, longer diabetes duration, high blood sugar, nerve damage, vitamin D deficiency) should be particularly attentive to foot health. Family members and caregivers of people with diabetes should also understand these risk factors to support prevention efforts.
Preventing foot complications is a long-term process. Improvements in blood sugar control can reduce nerve damage progression over months to years. Vitamin D supplementation effects may be seen within weeks to months. The benefits of smoking cessation for foot health accumulate over months and years. Regular foot screening and early detection of problems can prevent progression from ulcers to amputation within weeks to months if caught early. Most people won’t see dramatic changes immediately, but consistent attention to these factors over months and years significantly reduces complication risk.
Frequently Asked Questions
What are the biggest risk factors for diabetic foot ulcers and amputations?
Kidney damage and eye damage from diabetes are the strongest predictors. Nerve damage in the feet, high blood sugar levels, vitamin D deficiency, male sex, older age, and smoking also significantly increase risk. These factors often work together to damage blood vessels and reduce foot protection.
Can I prevent diabetic foot complications if I have diabetes?
Yes, many risk factors are modifiable. Maintaining good blood sugar control, getting adequate vitamin D, stopping smoking, taking medications as prescribed, attending all medical appointments, and performing regular foot self-exams can substantially reduce your risk of serious complications.
How often should someone with diabetes get their feet checked by a doctor?
The research supports regular professional foot exams, though specific frequency depends on your individual risk factors. People with nerve damage, previous ulcers, or multiple risk factors typically need more frequent exams. Discuss with your healthcare provider whether you need exams every 6 months, annually, or more frequently.
Does vitamin D deficiency really increase foot complication risk in diabetes?
Research shows vitamin D deficiency below 50 nmol/L has strong evidence linking it to foot complications. Maintaining adequate vitamin D through diet, supplementation, or sun exposure as recommended by your doctor may help reduce risk, though more research is needed on optimal levels.
Why does smoking increase the risk of amputation in people with diabetes?
Smoking damages blood vessels and reduces blood flow to the feet, making it harder for wounds to heal and infections to resolve. Combined with diabetes-related blood vessel damage, smoking significantly increases the risk that foot ulcers progress to amputation rather than healing.
Want to Apply This Research?
- Track weekly foot self-examinations (checking for redness, swelling, cuts, or sores), monthly HbA1c targets, vitamin D supplementation adherence, smoking status, and appointment attendance. Set reminders for professional foot exams every 6-12 months.
- Use the app to set daily reminders for blood sugar monitoring, weekly foot inspection checklists, medication adherence tracking, and smoking reduction goals. Create alerts for upcoming eye exams, kidney function tests, and podiatry appointments. Log vitamin D supplementation and track dietary sources of vitamin D.
- Establish a baseline assessment of your current risk factors with your healthcare provider. Use the app to track changes in modifiable factors (blood sugar control, vitamin D levels, smoking status, medication adherence) monthly. Share monthly summaries with your healthcare team to adjust prevention strategies as needed. Flag any new foot symptoms immediately for professional evaluation.
This article summarizes research findings and should not replace professional medical advice. If you have diabetes or are experiencing foot problems, consult with your healthcare provider or a podiatrist for personalized evaluation and treatment. The risk factors identified in this research are associations, not guarantees—having one or more risk factors does not mean you will definitely develop foot complications. Conversely, not having these risk factors does not eliminate the possibility of complications. Always follow your healthcare provider’s recommendations for diabetes management, foot care, and screening.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.