Researchers studied over 66,000 women with early-stage kidney disease who didn’t have anemia to understand how iron levels in the blood affect their health over 5 years. They found something surprising: women with lower iron levels had better kidney function and fewer serious infections, but were at slightly higher risk for bone fractures. Women with adequate iron levels faced more kidney problems and infections. These findings suggest that iron levels might be an important clue for predicting how kidney disease will progress in women, especially after menopause.

The Quick Take

  • What they studied: Whether iron levels in the blood can predict kidney disease progression and other health problems in women with early-stage kidney disease who don’t have anemia
  • Who participated: 66,768 adult women with stage 3 chronic kidney disease (moderate kidney function loss), normal blood counts, and normal red blood cell size. Researchers compared women with low iron levels to those with adequate iron levels.
  • Key finding: Over 5 years, women with low iron levels had about 9-10% lower risk of kidney disease getting worse and lower risk of serious infections compared to women with adequate iron. However, women with low iron had slightly higher fracture risk.
  • What it means for you: If you’re a woman with early-stage kidney disease, your doctor might use iron level tests to help predict how your kidneys will do over time. This is especially useful information for postmenopausal women. However, these findings need to be confirmed in other studies before changing standard medical practice.

The Research Details

This was a retrospective cohort study, which means researchers looked back at medical records from a large database (TriNetX) of women who already had stage 3 chronic kidney disease. They divided the women into two groups based on their iron levels and then tracked what health problems each group experienced over 5 years. To make the groups as similar as possible (except for iron levels), researchers used a statistical technique called propensity score matching, which is like pairing up women with similar characteristics but different iron levels.

The researchers only included women who had normal blood counts and normal red blood cell size, even though they had low iron. This is important because it means the women didn’t have anemia (low red blood cells), which made it easier to study iron’s effects separately from other blood problems.

The study tracked several health outcomes including acute kidney injury (sudden kidney damage), progression of kidney disease, infections like pneumonia, and bone fractures over the 5-year period.

This research approach is important because it uses real-world medical data from a very large number of patients, which gives stronger evidence than smaller studies. By matching women with similar characteristics but different iron levels, the researchers could better isolate iron’s specific effects. Understanding how iron affects kidney disease progression in women without anemia is valuable because most previous research focused on anemic patients, leaving a gap in knowledge.

Strengths: Very large sample size (66,768 women) provides strong statistical power; propensity score matching helps reduce bias; 5-year follow-up period is long enough to see meaningful health changes; published in a peer-reviewed journal. Limitations: This is an observational study, not a controlled experiment, so we can’t prove iron causes these effects; the study only included women, so results may not apply to men; some important health information may be missing from medical records; the study was conducted in a specific healthcare database, which may not represent all populations equally.

What the Results Show

Women with low iron levels had significantly better kidney outcomes over 5 years compared to women with adequate iron levels. Specifically, low iron was associated with about 9% lower risk of acute kidney injury (sudden kidney damage), about 5% lower risk of kidney disease getting worse, and about 4% lower risk of pneumonia infections.

These protective effects were even stronger in certain groups of women. Postmenopausal women with low iron showed the most benefit for kidney protection. Women aged 18-64 also showed clear benefits. Women with adequate vitamin D levels (≥30 ng/ml) and women with diabetes also showed stronger kidney protection when they had low iron.

However, the study also found a trade-off: women with low iron had higher fracture risk compared to women with adequate iron. This was particularly concerning in older women (over 65 years old) and those with low vitamin D levels.

The kidney disease progression risk decreased gradually over the 5-year period in women with low iron, with the difference becoming more pronounced each year (about 9-11% lower risk by year 5).

The study found that the relationship between iron levels and health outcomes varied significantly depending on other factors. For example, adequate iron levels were protective against fractures in older adults and those with vitamin D deficiency, suggesting that iron may play a role in bone health. The benefits of low iron for kidney protection were most pronounced in postmenopausal women, suggesting that hormonal status may influence how iron affects kidney function. Women with diabetes showed stronger kidney protection with low iron levels, indicating that iron’s effects may interact with blood sugar control.

Previous research has shown that iron deficiency and inflammation are common in kidney disease patients, but most studies focused on anemic patients (those with low red blood cells). This study is unique because it examined non-anemic women with low iron, filling an important gap in the research. The finding that low iron may protect kidney function in non-anemic women is somewhat unexpected and contrasts with the typical view that iron deficiency is always harmful. This suggests that the relationship between iron and kidney health is more complex than previously understood.

Important limitations include: the study only included women, so results may not apply to men; it’s observational, meaning we can’t prove low iron causes better kidney outcomes, only that they’re associated; the study couldn’t account for all possible factors affecting kidney health; results come from one healthcare database and may not represent all populations; the study didn’t measure all types of iron in the blood, only serum ferritin; women were already diagnosed with kidney disease, so results may not apply to people without kidney disease; some health outcomes were tracked through medical records, which may be incomplete.

The Bottom Line

For women with stage 3 chronic kidney disease: Iron level testing may provide useful information about kidney disease progression risk, particularly for postmenopausal women (moderate confidence). However, iron supplementation decisions should not be made based solely on this study—discuss with your doctor about your individual situation. For older women (over 65) or those with vitamin D deficiency, maintaining adequate iron levels may be important for bone health. These findings are preliminary and should be confirmed by additional research before changing standard medical practice.

This research is most relevant to: women with stage 3 chronic kidney disease; postmenopausal women with kidney disease; women with kidney disease and diabetes; healthcare providers managing kidney disease in women. This research is less directly applicable to: men with kidney disease; women with anemia; people without kidney disease; women with stage 1, 2, 4, or 5 kidney disease (different stages may have different patterns).

Health benefits or risks from iron levels typically develop over months to years. The study tracked outcomes over 5 years, so meaningful changes in kidney function or disease progression would likely take several years to become apparent. Bone fracture risk may develop more gradually over time, especially in older women.

Want to Apply This Research?

  • If you have stage 3 kidney disease, track your iron level test results (serum ferritin) every 3-6 months alongside your kidney function tests (creatinine and eGFR). Record the date, value, and any symptoms like fatigue or shortness of breath to identify patterns over time.
  • Work with your healthcare provider to monitor iron levels as part of your kidney disease management plan. If you have low iron, discuss whether supplementation is appropriate for your situation. Ensure adequate vitamin D intake (through sunlight, food, or supplements as recommended by your doctor) since vitamin D status appears to influence how iron affects kidney health.
  • Establish a long-term tracking system that includes: quarterly iron level tests; semi-annual kidney function tests; annual bone health assessment (especially if over 65); vitamin D level checks twice yearly. Share these results with your healthcare team to identify trends and adjust treatment plans accordingly. Note any changes in energy levels, bone pain, or kidney-related symptoms.

This research is observational and cannot prove that iron levels cause kidney disease outcomes. These findings apply specifically to women with stage 3 chronic kidney disease and may not apply to men, people with other stages of kidney disease, or people without kidney disease. Do not make changes to iron supplementation or other treatments based on this study alone. Always consult with your healthcare provider before making medical decisions. This information is for educational purposes and should not replace professional medical advice. If you have kidney disease, work with your nephrologist (kidney specialist) to develop an appropriate treatment plan based on your individual health situation.