Nutrition tips for older runners training in hot weather

The 2007 Chicago Marathon started in heat that reached 88 degrees, a record for the race, and organizers shut down the second half of the course three hours after the start. About 10,000 of the 45,000 registered runners stayed home, another 10,934 started and did not finish and aid stations ran short of fluids.

Heat of that kind is harder on older runners. In laboratory studies, adults aged 55 to 73 stored about 80% more body heat than young adults during three hours of resting heat exposure, because sweating and blood flow to the skin respond less strongly with age.

Here is how older runners training in hot weather can thrive.

Planned drinking before runs

Thirst is a weaker signal after 60. A review of age and fluid intake found that older adults challenged by exercise in a warm environment felt less thirsty and drank less than younger adults, and that their fluid balance took longer to recover. An older runner can be short of fluid at the start of a hot run without feeling it.

A glass of fluid with each meal and another 1 to 2 cups in the hour before a summer run keeps the runner from starting behind. Urine color on waking is a quick check. Dark urine is a sign to drink more before heading out.

The plan is meant to replace what the day and the run cost, and drinking far beyond that has its own risks on long efforts.

Heat and stored glycogen

A summer long run uses up stored carbohydrate faster than the same route in cooler months.

In a study of trained men cycling for 40 minutes at a hard but steady effort, muscle glycogen use was higher at 104 degrees than at 68 degrees. Follow-up laboratory work found that heat also reduced how much of the carbohydrate eaten during exercise the body put to use, and the muscles used more of their own stored glycogen.

A carbohydrate-rich dinner the night before and a small snack or breakfast before an early start leave more in reserve, and a shorter route on the hottest days uses fewer carbs.

Sodium in meals and drinks

Many older runners follow a lower-sodium diet for blood pressure.

The American Heart Association sets an upper limit of 2,300 milligrams of sodium a day for most adults, with 1,500 milligrams as the ideal target. Long runs in the heat add sweat losses on top of daily needs, and the two goals can conflict.

Sodium can be planned around the long runs instead of spread across every day. For runs longer than an hour in the heat, runners can buy hydration drinks that list sodium on the label or eat a salted snack beforehand. A runner on a sodium-restricted diet or blood pressure medication should agree on an amount with their doctor first.

Pre-run cooling with ice slurry

Ice slurry, a blend of crushed ice and liquid, absorbs heat as it melts in the stomach, so drinking it lowers core temperature before the run starts.

That gives the runner more time before body temperature limits the pace on a hot day. In a study of 10 men running in 93-degree heat, drinking 7.5 grams per kilogram of ice slurry beforehand extended running time to about 50 minutes, compared with about 41 minutes after the same amount of cold water. Core temperature at the point of exhaustion was also higher after the slurry, meaning the runners tolerated more heat before stopping. The study did not include older runners.

For a runner weighing 155 pounds or 70 kilograms, the dose works out to about 18 ounces, taken shortly before the run. A blender with ice and diluted fruit juice makes a home version. Runners who find a full dose uncomfortable can start with half of it on a cooler day and build up.

Water-rich foods and daily totals

The National Academies set dietary intake levels for total water at about 3.7 liters a day for men and 2.7 liters for women, with roughly a fifth coming from food. The panel also noted that highly active people in hot conditions may need 6 liters or more.

Watermelon, cucumbers, oranges and soups raise the food share without adding much bulk.

Coffee, tea, and milk also count toward the total, which matters for older runners who find large amounts of plain water hard to drink.

Medication review before summer training

Several drugs common in older adults change the body’s response to heat.

Diuretics and ACE inhibitors or angiotensin receptor blockers lower blood pressure while increasing urinary water loss or reducing thirst, which raises the risk of heat illness on a summer run. Beta blockers reduce sweating and blood flow to the skin.

Anticholinergic drugs, used for bladder and other conditions, also reduce sweating. A runner taking any of these should ask a doctor or pharmacist before the summer training block begins, since doses or run timing may need to change. Running in the cooler hours and carrying fluid become more important for this group.

Heat acclimatization over 7 to 14 days

Older bodies still adapt to heat.

In a study of 15 adults aged 60 to 78 and 16 adults aged 21 to 40, seven days of 90-minute hot baths at 40 degrees Celsius (104 degrees Farhenheit) made the nerve signals for sweating and skin blood flow switch on sooner. The changes were similar in both age groups.

For runners, the same adaptation comes from training in the heat.

Reviews of heat acclimation put the most complete response at 7 to 14 days of repeated exposure, with about 80% of the benefit possible in 4 to 7 days.

Three days of heat exposure produced no measurable benefit in young or older women in one study, and women may need more days or longer sessions than men to adapt. Short, easy runs in the warmer part of the day for the first week or two, with fluid on hand, are a safer start than a long run on the first hot weekend.

Lessons from a hot marathon

The Chicago Marathon was known for brisk fall weather. Before 2007 its temperature record was 84 degrees, set in 1979. That October, the heat passed the old mark by 4 degrees and fluids ran short on the course, and at least 49 runners were hospitalized while 250 more were treated on site.

A fall race can still bring summer conditions, and the heat training and fueling habits built in July and August are what an older runner brings to a day like that.