I am on the twitter and I came across this tweet:
The tweet reads, “It annoys us at The Kidney Group when so-called experts claim being well-hydrated is overrated and without much merit. Completely untrue.”
The fact is this is total bullshit. Outside of patients with kidney stones or pre-renal azotemia, I am aware of no human data showing improved kidney function from increased fluid intake. In fact in the MDRD study they found an association with high fluid intake and faster progression to dialysis. Having a 24-hour urine volume of 2.4 liters was associated with a loss of kidney function of 1 ml/min/year faster than patients with a urine output of 1.4 liters.
In a comprehensive study on the risk factors for the development of ESRD (PDF) (27+ years of follow-up of 177,570 patients) having nocturia (HR 1.36) was about as important a risk factor as anemia (HR 1.33) or family history of kidney disease (HR 1.40) on multivariate analysis.
The authors take on the significance of nocturia:
It is interesting that nocturia (defined herein as self-report of “always having to interrupt sleep to urinate”) emerged as an independent risk factor for ESRD because it is a widely held clinical belief that nocturnal polyuria is an early sign of chronic kidney disease due to decreased urinary concentrating ability, although some data suggest that increased salt, not water excretion, is more important. Therefore, nocturia may reflect subtle early renal disease not captured by serum creatinine level or urine dipstick analysis. We also cannot exclude the possibility that nocturia reflects undiagnosed DM. An alternative hypothesis is that nocturia reflects a high volume of ingested fluid that is detrimental (especially among patients with existing kidney disease), as high urine volume increases intratubular volume and pressure and these stretch forces induce fibrosis. Practically speaking, our data lend no support to the notion that a high volume of water intake should be recommended in clinical practice as being beneficial to kidney function.
For a summary of the myth of water intake and kidney health look at this excellent review by Wenzel et al in CJASN (PDF).
“It annoys us at The Kidney Group when so-called experts claim being well-hydrated is overrated and without much merit. Completely untrue.”
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And this comes by way of Fort Lauderdale, Florida’s “Best Nephrology Practice giving up-to-the-minute practical advice to keep your kidneys healthy.”
Scary.
My friend Dan Negoianu (a renal fellow when I was a resident at U. Penn) also wrote this JASN commentary which speaks to the same lack of evidence for recommendating increased water intake.
http://jasn.asnjournals.org/cgi/content/full/19/6/1041
You might also enjoy Lette & Dwyer's "The Fluid Craze" in Lancet (Sept 2008).
(I know I just stuck a comment on another post of yours claiming I ought to be asleep by now, but I had to comment on this.)
Drinking a LOT of water is now being recommended to polycystic kidney disease patients by some nephrologists because of relatively recent discoveries about the role of vasopressin and cAMP in cyst growth. There’s a clinical trial on currently using Tolvaptan to inhibit vasopressin, as well another where they’re trying to figure out just how much water you need to drink to suppress vasopressin enough to slow or stop cyst growth. Tolvaptan or large volumes of water were very successful in slowing or stopping cysts in animal models of PKD. So some nephrologists, in patients whom they’ve determined it to be safe, are recommending higher water intake.
http://jasn.asnjournals.org/cgi/content/abstract/19/1/102
Lena,
I eagerly await the data from the tolvaptan trial and in the meantime I tell my patients to drink a lot of water. But you must be cautious because the MDRD trial had a significant number of PKD patients, and when they analyzed how those patients did when stratified by urine output they found PKD patients had an even larger negative effect from increased urine output. So we need to temper our enthusiasm for water drinking while we wait for the human data.
Thanks for all of your insightful comments.
A retrospective analysis of the MDRD study (139 participants
with and 442 without ADPKD; GFR at entry 25 to 55 ml/min
per 1.73 m2) was performed to examine the relationship be-
tween fluid intake (reflected by 24-h urine volume and urine
osmolality) and renal disease progression. Higher urine vol-
umes and lower urine osmolalities were associated with faster
GFR decline regardless of whether the patient had ADPKD.
The authors considered two possible explanations. The first
was that excessive fluid intake and high urine volume cause
faster renal disease progression and possibly cyst growth in
ADPKD. The second was that high urine volume with low
urine osmolality is the result and not the cause of faster renal
disease progression (19). The results by Nagao et al. (18) do not
support the first explanation; on the contrary, they suggest that
increased fluid intake may be beneficial to some patients with
ADPKD, at least in early stages of the disease.
The rest of the article is here:
http://jasn.asnjournals.org/cgi/reprint/jnephrol;17/8/2089