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Our most recent book has answers to the 200 most common questions that readers have asked us over the 19 years since this site began. Get it here: Your Diabetes Questions Answered
Diabetic Kidney Disease
One of the worst things high blood sugars do to your body is that they slowly destroy your kidneys.
Unfortunately, as is the case with so many "diabetic" complications, this organ destruction also appears to begin long before many people are given a diabetes diagnosis.
The landmark UKPDS study found that one out of eight people diagnosed with diabetes already were leaking small amounts of protein into their urine. This symptom, called "microalbuminuria." is an early sign that kidneys have been damaged.
Though there is no total agreement as to why this occurs, some factors that promote kidney damage are:
1. High blood pressure. When blood pressure is high, large protein molecules, including those that are glycosylated (covered with sticky excess sugar molecules) are pushed through the pores of the kidney's filtration units, damaging them.
2. High blood sugar. When normal glucose regulation fails, the kidneys must remove excess glucose from the blood, leading to high concentrations of glucose in the kidneys. These glucose molecules clog up tiny capillaries in the kidneys as they do those elsewhere in the body. Eventually this clogging destroys the glomeruli, the filtration units of the kidney.
An eleven year study of over 1800 people with diabetes found a straight line relationship between the risk of developing chronic kidney disease and the A1c. The risk began to increase significantly when the A1c rose over 6.0%.
Poor Glycemic Control in Diabetes and the Risk of Incident Chronic Kidney Disease Even in the Absence of Albuminuria and Retinopathy: Atherosclerosis Risk in Communities (ARIC) Study. Lori D. Bash et al. Arch Intern Med. Vol. 168 No. 22, Dec 8/22, 2008
Another study, that followed people with Type 1 diabetes for more than a decade found that those who had achieved "Tight control" in the DCCT (defined as A1cs near 7%) had half the risk of developing the condition leading to kidney failure than those who did not. The full text article explains that it took ten years for the impact of that early tight control to become evident.
Lower A1cs, in the 5% range--which are easier for people with Type 2 to achieve than for those with Type 1--would likely reduce this risk a lot further.
Intensive Diabetes Therapy and Glomerular Filtration Rate in Type 1 Diabetes: The DCCT/EDIC Research Group New England Journal of Medicine, November 12, 2011 (10.1056/NEJMoa1111732)
3. Painkillers. Unfortunately for a generation hooked on "Vitamin I" it turns out that long term use of Ibuprofen, and Tylenol can all damage kidneys severely.
There is some suggestion that the risk goes up as the lifetime dose goes up. taking one thousand pills of Tylenol per lifetime, for example, appears to up your risk of kidney failure significantly, as does taking 5000 NSAID pills.
Analgesic Nephropathy - NIH NIDDK
4. Sodium Phosphate Colon Cleansing Drugs combined with ACE inhibitors or ARBs.This drug, prescribed to cleanse the colon before colonoscopy, can cause acute and permanent kidney failure in people who are taking common blood pressure medicines.
Acute Phosphate Nephropathy following Oral Sodium Phosphate Bowel Purgative: An Underrecognized Cause of Chronic Renal Failure. Glen S. Markowitz, M. Barry Stokes, Jai Radhakrishnan, Vivette D., D'Agati. JASN doi: 10.1681/ASN.2005050496
5. Strong Fluctuations in Blood Sugar. An in vitro study (that is, a study done on tissue in the lab, not live people) found that exposing kidney cells to blood sugar levels that fluctuated between 135 mg/dl and 270 mg/dl did more damage to those cell--in terms of causing growth of fibrous tissue--than constant exposure to the high blood sugars. The explanation given involved osmotic changes caused by the fluctuations as well as the suppression of some expression of genes that countered the growth of fibrous tissue when exposed to high blood sugars in a steady state.
Of note in this study, too, are the many graphs showing that a steady exposure to blood sugars of only 135 mg/dl was almost the same as exposure to a steady normal blood sugar level of 90 mg/dl in terms of spurring the growth of fibrous tissue in the kidney. It is fibrous tissue that destroys kidney function.
The authors conclude,
These results support the recommendation for postprandial monitoring of glucose levels in patients with diabetes mellitus and imply that important differences in end organ damage could occur in individuals with similar HbA1c but different postprandial glucose levels.
They go on to explain that their findings prove that it is not glycation (the attachment of glucose molecules to proteins), as is usually believed, that destroys the kidney tissue so much as the effect of the fluctuations of blood sugar on gene expression. They urge more attention to eliminating spikes.
Short-term peaks in glucose promote renal fibrogenesis independently of total glucose exposure. T. S. Polhill, S. Saad P. Poronnik,G. R. Fulcher, and C. A. Pollock. Am J Physiol Renal Physiol 287: F268-F273, 2004.
6. Coke, Pepsi and other cola drinks with Phosphoric Acid. A July 2007 study found that two cola drinks a day, whether regular or diet, doubled the risk of kidney damage. The culprit is apparently the phosporic acid (which also leaches calcium out of bones and promotes osteoporosis.) Sodas with citric acid did not worsen kidney disease.
As a person with diabetes you already have enough risk factors to consider, why make things worse with these dangerous cola drinks!
Carbonated Beverages and Chronic Kidney Disease. Saldana, Tina M.; Basso, Olga; Darden, Rebecca; Sandler, Dale P.. Epidemiology. 18(4):501-506, July 2007.
7. Foods with Added Phosphates. The same phosphate that is damaging when you consume brown sodas is found in many other processed meats and dairy products, baking powder, and are found in the pill bases used for many supplements. Read about the problems caused by consuming these dangerous additives HERE.
8. Other Potentially Dangerous Pharmaceutical Drugs. The following prescription medications are capable of causing problems in people who already have significant kidney damage:
a. ACE inhibitors and ARBs. These drugs protect the kidneys in most people, but if you have a condition called "renal artery stenosis" they may be harmful.There is a test, the Captopril Scan, that can be done to ensure you respond appropriately to these kinds of drugs if there is any question that you might have renal arterial stenosis.
b. Radioacontrast agents used during angiography. According to this review published in Endocrine Today up to 35% of people with diabetes may experience acute renal failure when given these during angiograms. Proper hydration appears to be the appropriate defense. Discuss this issue with your doctor before you find yourself in a hospital having tests done by doctors who don't have your chart. If you are at risk, make sure that information is available at any hospital you might be taken to.
c. Antibiotics. These can occasionally cause kidney failure, too. Again, this is mainly a problem if you have serious kidney damage. If you do ask the doctor who treats your diabetes--or a registered pharmacist--if an antibiotic is safe for you before you take ANY medication prescribed by another doctor who may not know the details of your case
Much of the above is summarized in this review: Endocrine Today: Medications that worsen renal function in diabetes
Does a Low Carb Diet Cause Kidney Damage?
The belief that high protein diets cause kidney damage is one reason why, for many years, doctors warned people with diabetes that low carb diets would kill their kidneys.
Fortunately, this turns out not to be true. While almost any intake of protein is a problem for people with advanced kidney disease, studies have found repeatedly that for people with normal kidney function or early diabetic changes the low carb diet does not promote kidney damage.
This was confirmed in a study published in 2012 of 307 obese individuals without kidney disease who were put on a low carb diet over a two year period. The study, which was published in a high profile journal intended for kidney specialists, concluded that the low carb diet did not cause noticeably harmful effects to patients' kidney function or their fluid and electrolyte balance compared with a low-fat diet.
Comparative Effects of Low-Carbohydrate High-Protein Versus Low-Fat Diets on the Kidney. Allon N. Friedman et al. Clinical Journal of the American Society of NephrologyMay 2012 doi: 10.2215/?CJN.11741111
People who are able to normalize their blood sugars with a low carb diet often report that their kidney function recovers and that microalbumin disappears from their urine. This effect has been observed in a published study.
A low-carbohydrate diet may prevent end-stage renal failure in type 2 diabetes. A case report. Jorgen Vesti Nielsen et al. .Nutr Metab . 2006; 3: 23.
One possible reason this may happen is because a low carb diet is really a high fat diet, not a high protein diet. While protein might make up a larger percentage of intake on a low carb diet, the actual amount of protein eaten is usually not all that different from that found in a low fat diet.
Think of it this way. If I eat a hamburger with no bun and no fries and a salad and you eat a hamburger, bun, and fries, my protein intake may be 50% of the calories I ingest, making it look like I'm eating a "high protein" diet. You are eating the same amount of protein, but the intake of all those high calorie carbohydrates makes your protein intake a much smaller percentage of your total calorie intake, so a nutritionist will consider this a safer, "lower protein" intake.
Meanwhile, someone eating a high carb diet has to contend with all the glucose from those carbohydrates that are routed through the kidneys, while the person eating the hamburger and salad will not because their blood sugar will not rise out of a normal range.
If you are really concerned about possible problems with a high protein diet and your kidneys there is a simple solution. Don't EAT a high protein diet. Eat a low carbohydrate diet with just enough protein to provide enough to repair your muscles and organs and provide the glucose needed to run your brain.
Use the Protein Calculator you'll find here to determine your exact protein need while eating a low carb diet. Just be careful that the meats and cheeses you eat on your healthy low carb diet are not the processed versions, filled with added inorganic phosphates that may be harmful.
A review of research evidence on the topic of whether low protein diets actually help people with diabetes preserve kidney function published in Sept of 2008 comes up with the suggestion that they do not and suggests that ACE inhibitors and ARBs are as effective.
An editorial discussing these findings points out that no research has been done to look into the impact of cutting carbs on the health of the diabetic kidney.
How to Learn How Healthy Your Kidneys Are
If you have abnormal blood sugars--caused by diagnosed diabetes or by pre-diabetes--your doctor should run a microalbumin test at least every year to watch for signs of early kidney damage.
The microalbumin test is a simple test that requires only that you provide a urine sample when you go to the lab.
Another more accurate test of kidney function is one where you collect an entire day's worth of urine which is then analyzed for protein. Few doctors will order this, but if yours does, congratulate yourself on finding doctor who is aware of what it takes to keep your kidneys healthy.
If your doctor doesn't order at least a microalbumin test for you, it is a good sign you need to find a new and more up to date doctor immediately!
A cheaper test doctors often run gives you your creatinine clearance rate and estimated GFR (a measure of how much filtering your kidneys are doing.) One problem with this is that when you have high blood sugars, you may for a while have a higher than normal GFR, which will NOT be detected by the simple test and will be considered normal.
Unfortunately, higher than normal GFRs caused by your body dumping lots and lots of glucose eventually give way to lowered GFRs which are a sign that your kidneys are on their way to failing. You don't want to wait for that test result to find out you are in trouble. The microalbumin test gives you an early warning you can put to good use since the damage it shows CAN be reduced or eliminated by normalizing your blood sugars.
Nephropathy in Diabetes American Diabetes Association Position Statement.Diabetes Care 27:S79-S83, 2004
What To Do If You Have Early Signs of Kidney Damage?
Normalizing your blood sugars will help reverse early kidney damage.
Normalizing means getting to truly normal--not the damagingly high blood sugar levels that the ADA and most doctors tell you are fine. If you let your A1c stay near 7% and only test your blood sugar when you first wake up, you can pretty much expect to see any kidney damage get much, much worse.
You must get your A1c under 6% and strive to lower it as close as you can to 5%. You do this mainly by keeping your post-meal blood sugars under 140 mg/dl at 2 hours after eating as often as possible.
You may be able to do this with a lower carb diet alone using the strategy described here. But most people with Type 2 diabetes will find that they need a combination of drugs that combat insulin resistance and insulin to achieve this.
Most importantly, you need a doctor who is committed to helping you achieve this. If your doctor is not willing to work with you to get to normal blood sugars when you show signs of early kidney disease you must find a doctor who will. Ideally such a doctor would be an endocrinologist who is a member of the American Association of Clinical Endocrinologists and endorses their recommendations for blood sugar control. But if you are unable to be treated by an endocrinologist a family doctor who keeps up to date, or who will work with you if YOU bring in the research supporting the blood sugars you want to achieve will work.
Vitamin B1 May Help
Research published in December of 2008 suggests that supplementation with Thiamine, Vitamin B1, may help fight diabetic kidney disease.
Patients taking 100 mg three times a day saw a 41% decrease in the amount of albumin excreted in their urine, which is believed to be an index to kidney damage.
High-dose thiamine therapy for patients with type 2 diabetes and microalbuminuria: a randomised, double-blind placebo-controlled pilot study. N. Rabbani et al. Diabetologia10.1007/s00125-008-1224-4, Dec 05, 2008.
Control Blood Pressure
ARBs and ACE inhibitors are believed to prevent kidney damage in people with diabetes better than diuretics like HCTZ and other classes of blood pressure medications. However, they may be dangerous if kidney damage is well advanced. There is a test your doctor can do, the captopril scan, which can determine if it is safe for you to take these drugs.
There is a generic ACE inhibitor on the market, lisinopril, which is more affordable for people on limited incomes. ARBs are often prescribed to people who cannot tolerate ACE inhibitors, That class of drugs includes losartan and valsartan.
Both these classes of drugs appear to lower insulin resistance by a small amount, too.
Avoid beta blockers, as they have been found to worsen blood sugar control. They also can turn off hypo awareness, which is very dangerous if you are using insulin.
Whatever it takes, you must keep your blood pressure as normal as possible if you have any signs of diabetic kidney disease.
Avoid Brown Sodas like Coke, Pepsi and Processed Foods with added Phosphates
The manufacturers will undoubtedly argue that one study isn't enough to damn their popular sodas, and that we should await further research. But because people with diabetes already are at risk for kidney disease, we should avoid anything that looks like it might further damage our kidneys, especially nutritionally worthless sodas which have already been implicated in weakening our bones.
Go EASY with Painkillers
Don't take painkillers like Tylenol or Ibuprofen (and other NSAIDS like Motrin, Aleve, and Celebrex) unless you really need them. When you do take them, avoid the "extra strength" sized pills and look for the lowest dose that will control your pain. You want to live a very long time and the troubling "lifetime dose" statistics of these drugs mean that they can be toxic to everyone, not just people with diabetes. Add their toxicity to the problems caused by diabetic blood sugars and you are looking at a formula for kidney loss.
Never use a Sodium Phosphate Drug before Colonoscopy
These drugs rarely can cause complete kidney failure. Why dice with fate. There are other preparations available that don't carry this risk. Make sure to demand one from your doctor if you go for a colonoscopy.
Do NOT Supplement with Higher than Normal Doses of Vitamins B6, B12 and Folic Acid
A study of people with both Type 1 and Type 2 diabetes who had been diagnosed with diabetic kidney disease found that supplementing daily with a "Single tablet of B vitamins containing folic acid (2.5 mg/d), vitamin B6 (25 mg/d), and vitamin B12 (1 mg/d)" for three years was associated with faster deterioration in GFR and a doubling of stroke risk.
Effect of B-Vitamin Therapy on Progression of Diabetic Nephropathy:A Randomized Controlled Trial. Andrew A. House et al. JAMA 2010;303(16):1603-1609. doi: 10.1001/jama.2010.490
It's important to note that the amounts used in this study were megadoses many times greater than the RDA (Recommended Daily Allowance) for each.
If you are eating a diet that does not include grains or other foods that supply natural forms of these vitamins you won't be getting them in your diet and will need to supplement, but when you do, confine your supplementation to the RDA. You can find the RDA for the B vitamins HERE.
Be Cautious About Taking Invokana, Jardience and Other Drugs in That Class
Some research suggests that the SGLT-2 family of drugs prescribed to control blood sugar (which they do poorly) do help prevent kidney failure as well as preventing heart attacks in people with heart failure.
But unless you have severe kidney disease, you are likely to end up much better off reversing your kidney damage by lowering your blood sugar to the range that provides 5% A1cs than you will by taking drugs with some very disturbing side effects.
What is "Spilling Sugar" and How Does It Relate to Kidney Damage
Each person has a certain blood sugar level at which the kidneys will start pulling glucose out of the blood stream and eliminating it in the urine. The average level at which this happens is around 180 mg/dl (10 mmol/l). In fact, before blood sugar meters became common, most doctors diagnosed type 2 diabetes using a urine dip, and patients "controlled" their blood sugar by testing their urine for glucose and feeling confident they were doing well if they didn't see any.
However, that 180 mg/dl threshold is only an average. Individuals vary greatly in where they, personally, will spill glucose into the urine.
Some people have forms of diabetes (particularly MODY-3) where they can spill glucose in urine at levels as low as 140 mg/dl.
Others of us, and I'm one of them, have forms of diabetes where glucose doesn't appear in the urine until our blood sugar goes over 250 mg/dl. (That is one reason I had to wait so many years to get a formal diagnosis. For decades my doctors only screened me for diabetes with a urine dip.)
It is possible that there is a relationship between how much glucose appears in the urine and your risk for kidney damage, though there isn't enough research to draw any conclusions. But if your renal threshold is unusually low, it makes sense to try to keep your blood sugar at a level low enough that you don't spill sugar, even if you are spilling at a level your doctor tells you is "nothing to worry about."