Published 2026-08-03 · OxalateWatch · Dietary reference, not medical advice

Athletes Are a Stone-Risk Group: The Hydration Lesson from the Tennis Tour

As the summer tennis hard-court season rolls on — and qualifiers were decided at a WTA 1000 event in early August — the athletes on court are a reminder of a counterintuitive fact: competitive athletes are a kidney stone risk group. Heavy training causes fluid and electrolyte losses through sweat, high-protein diets and some supplements raise stone-relevant urine chemistry, and the travel lifestyle makes consistent hydration hard. The hydration discipline that keeps an athlete on court is the same discipline that prevents stones in everyone else.

Stone risk in athletes is documented in the sports medicine literature: endurance athletes, military trainees in hot environments, and team-sport players show elevated stone rates in some cohorts, with chronic low-grade dehydration and concentrated urine as the suspected drivers. The athlete's lesson transfers directly to the desk worker, the weekend hiker, and the summer gardener — sweat losses must be replaced, and urine should stay dilute.

The Athlete's Stone-Relevant Variables

• Sweat losses. High sweat rates reduce urine volume, concentrating calcium, oxalate, and uric acid.
• Protein-heavy training diets. High animal-protein intakes can lower urinary pH and citrate, favoring uric acid and mixed stones.
• Supplements. Vitamin C megadoses, creatine, and some protein powders have been linked in research to changes in stone-relevant urine values.
• Travel and routine disruption. Hotel rooms, tournament schedules, and long flights make water intake an afterthought.

What Athletes (and the Rest of Us) Should Drink

The athlete's hydration stack is simple: water as the base, an unsweetened electrolyte drink when sweat losses are heavy, coconut water or orange juice as a natural option, and the high-oxalate drinks (strong tea) kept modest. The sugar-sweetened sports drink is the trap — it hydrates and adds a sugar load that the research links to stone risk.

Beyond Fluids: The Athlete's Diet Check

Hydration is the headline, but the athlete's stone profile has dietary pieces too:

• Calcium at meals. Heavy training diets that cut dairy for weight or convenience lose the oxalate-binding calcium. Milk or yogurt after training covers it.
• Protein portioned, not doubled. Protein supports muscle — and excess animal protein shifts urine chemistry. Palm-sized portions at meals are the stone-aware version.
• Supplements reviewed. Vitamin C megadoses convert to oxalate; creatine and some protein powders deserve a stone-aware review with a clinician.
• Urine color as a gauge. Pale straw means hydration is working; dark amber means more water, now.

What the Research Does and Does Not Say

The tennis tournament itself is a sports event, not a study. The stone relevance comes from the broader sports-medicine literature on athletes and stone risk — elevated rates in some active populations, with dehydration as the leading suspected mechanism. No single event proves anything; the pattern across training populations is the signal, and the lesson — replace sweat, dilute urine, keep calcium — applies to athletes and non-athletes alike.

The Bottom Line

Competitive athletes face elevated stone risk because their lifestyle fights hydration and urine dilution — and the same is true of anyone who sweats heavily, travels, or skips water on busy days. The fix is the same for a tour player and a summer hiker: water as the base, electrolytes when sweat is heavy, calcium at meals, protein in palm-sized portions, and supplements reviewed. Hydration is the cheapest performance enhancer — and the cheapest stone prevention.

Quick Takeaway

Sweat concentrates urine, and concentrated urine makes stones. Replace fluids, keep calcium at meals, portion the protein —

There is a useful mental model from sports science called 'planned drinking' — hydrating on a schedule rather than by thirst. Thirst is a lagging signal: by the time you feel it, performance is already slipping, and urine is already concentrating. The same applies to stone prevention. A planned approach looks like this: a glass of water on waking, one with each meal, one mid-morning and mid-afternoon, and extra after any sweat. Athletes use the schedule because it works; stone patients can borrow it directly. Urine color is the athlete's gauge and yours — pale straw means the plan is working, and dark amber means the schedule needs to tighten. The discipline is identical,

Finally, a word on recovery nutrition for active people: the post-workout meal is the natural place to put the calcium back. Milk, yogurt, or a cheese-and-crackers snack after training replaces fluid, adds protein, and delivers the oxalate-binding calcium that sweat-heavy days often lack. Active people who skip dairy in training diets are stacking two stone risks — dehydration plus low calcium — when a post-exercise glass of milk addresses both. It is the cheapest recovery drink and the cheapest stone prevention available,

That is the whole athlete's edge in two sentences: replace what sweat takes, and put the calcium back with the same meal. Those two habits, repeated daily, are what keep an athlete's kidneys — and anyone's — out of the stone clinic. Everything else — the electrolyte drinks, the timing, the supplements — is detail on top of those two habits.