Sweat, Mineral, and Micronutrient Losses Related to Hiking in Higher Temperatures

When hiking in higher temperatures, it’s possible for you to incur significant fluid loss through sweat. However your sweat can also have important amounts of electrolytes in it, and even vitamins and minerals, especially if you’re not acclimated to the heat. Thus it’s imperative for hikers, backpackers, and thru-hikers to know what losses occur when, so they can replete there stores to maximize their health on the trail.

It’s summer time once again, here in Southern California, and that means hiking in 85-100F temperatures on dry, sunny trails, in want of shade. Let’s see what we need to know.

Sweating Basics Related to Hiking

There is a lot of variability regarding average sweat rates in the sports medicine literature (0.5L to 2L per hour), making it unhelpful in planning your rehydration. See the section ‘What is a normal sweat rate?’ in my article How To Calculate Your Sweat Rate
There is significant variability in your sweat rate, just based on your pre-hike hydration levels. You will have a delayed onset of skin vasodilation and sweating if you start your hike dehydrated.
There is significant variability regarding your personal sweat rate, as a function of how acclimated to the heat your are. Sweat rate increases after 10-14 days of heat exposure. You will tend to sweat more if you regularly work outdoors or in a hot indoor occupational setting like a steel mill, and if you don’t have air conditioning in hot Southern California.
As ambient air temperatures increase, your body’s ability to get rid of heat through conduction, convection, and radiation becomes defeated. The only way to dissipate your body heat at higher temps is through sweat evaporation. In dry climates like Southern California, evaporation can account for up to 98% of heat loss at higher temps.
One can sweat to the point of dehydration and as a result, this can disrupt their thermoregulatory function, and raise their core temperature at a rate of 0.27 to 0.36F for every 1% loss of body weight due to sweat.
Mineral (i.e. electrolyte) and micronutrient losses can be significant, especially in the initial days of hot weather for people not acclimated to the heat, and especially on longer hikes (those exceeding 4 hours in length).
The only way to estimate your sweat rate is through pre and post-hike measurement of your body weight, and measurement of any fluid you took in, or urine produced between those two body weight measurements.

Electrolyte and Mineral Related Losses in Sweat During Hiking

After sweat loss, electrolyte losses through sweat are the most pressing concern, when hiking at higher temperatures. Thru-hikers and backpackers may often replenish their fluid losses from sweat, but forget to continue to replenish their sodium losses, putting them at risk of hypervolemic hyponatremia, with its neurological consequences. This is less of a concern when day hiking, but could be so on a longer, more strenuous hike.

Electrolyte concentrations in sweat are similar for different sexes and ages

Medscape.com tells us that, “Neither sex, maturation, or aging appear to have marked effects on sweat electrolyte concentrations,” under their article, Exercise and Fluid Replacement.

Keep that in mind as you read over the individual electrolyte facts:

Sodium

There is significant variability in the amount of sodium lost through sweat with 200mg to 2,300mg per liter (0.2-2.3g/L) being on the extremes. (the lower extreme = likely someone perfectly acclimated to the heat; the higher extreme = likely someone with a high salt diet)
According to the article “Does Replacing Sodium Excreted in Sweat Attenuate the Health Benefits of Physical Activity?” in the International Journal of Sport Nutrition and Exercise Metabolism, sweat typically contains 40-60mmol/L of sodium, which translates to 0.92-1.38g/L of sodium.
According to the article “Relationships between micronutrient losses in sweat and blood pressure among heat-exposed steelworkers” in the NIOSH journal, Industrial Health, 102 workers working at ambient air temps of 86 to 95F had an average sodium content in their sweat of 1.08g/L during their regular 8 hour shifts at their steel working jobs.
During novel heat exposure (first 3 to 5 days of summer temperature hiking, for instance) sodium lost through sweat will be higher, but will decrease after 5-10 days of heat exposure as the body acclimates. It is possible during this 3 to 5 day novel heat exposure period, and increase in sodium intake may be needed, especially during long hiking excursions (4-8 hours of hiking).
Using a hydration solution that contains 300-700mg of sodium per liter (for example Gatorade has 450mg/L) should be considered under the following conditions: the hiker is sick and missed or vomited a meal, or there was no access to a meal; the hiker is hiking more than 4 hours; the hiker is hiking in the initial few days of hot weather, before acclimation to such, as stated above.
During longer hikes, or high sweat volume hikes before hot weather acclimation, where no sodium infused hydration solution is available, but only water, hikers should consider higher sodium backpacking foods to replete their losses.
Once acclimated to higher temp and heavy sweating environments, the body can reduce sodium loss through sweat to as low as 3-10mmol/L or 0.069-0.23g/L.
High sodium sweaters may be individuals with high dietary intakes of sodium
Hikers should be careful to not excessively over consume plain water on longer hikes that don’t end up producing equivalent sweat volumes, as such can lead to hypervolemic hyponatremia. If one’s plasma sodium falls at a rapid rate, such can induces seizures and other neurological symptoms. Hikers may elect to use a hydration solution with proper sodium in it to minimize this risk, and also be cognizant of their sweat rates under different conditions.

Potassium

there is less variability regarding potassium losses in sweat. According to the company, Horbia, who manufactures instruments to measure sweat electrolytes, the normal range sweat potassium falls into is 2-10mmol/L or 0.078-0.39g/L, which is 78-390mg/L.
According to www.sportsrd.org sweat has 160-390mg/L of potassium.
Referencing the same study as above, “Relationships between micronutrient losses in sweat and blood pressure among heat-exposed steelworkers” in the NIOSH journal, Industrial Health, our 102 steel workers working in 86-95F ambient air temps for 8 hours, at their regular jobs, sweated on average 160mg/L of potassium. Keep in mind these people are acclimated to hot work conditions.
medscape.com says that average potassium concentrations in sweat are 5mEq/L or 195mg/L.
Generally your kidneys chill out during exercise, so if your only producing 0.5ml/kg/hr of urine, with an average concentration of potassium of 20mEq, then for a 70kg adult producing 0.105L of urine on a 3 hour hike, which contains 2.1mEq of potassium, their urinary potassium loss of 82mg could be significantly exceeded by what they’ve lost through sweating.
Gatorade, which contains 125mg/L of potassium has the ability to replete a good amount of potassium lost through sweating, as long as your hike is only a few hours long.
Post hike repletion via diet is likely sufficient for day hiking for a few hours in higher temps. For example the Backpacker’s Pantry dehydrated backpacking food I’m examining on my Gluten Free Backpacking Hot Foods article have 1,000-1300mg potassium per bag and can be used for both macro and electrolyte post-hike repletion with regard to sodium and potassium.

Calcium, Magnesium, and Chloride

	Chloride	Magnesium	Calcium
Average Concentration in Sweat	30mEq/L	0.8mEq/L	1mEq/L
Average Concentration in Sweat (mg conversion)	1,064mg/L	9.7mg/L	20mg/L
Concentration Range in Sweat	5-60mEq/L	0.2-1.5mEq/L	0.3-2mEq/L
Concentration Range in Sweat (mg conversion)	177-2,127mg/L	2.4mg-18mg/L	6-40mg/L

Average concentrations and concentration ranges for Chloride, Magnesium, and Calcium in Sweat (mobile users scroll left and right)

Chloride is another heavy loss electrolyte in sweat; along with sodium and potassium, it helps regulate fluid balance.
Chloride also helps regulate the body’s pH. When I was studying for my Certified Nutrition Support Clinician exam, it was important to balance the chloride and acetate going into a parenteral nutrition bag, when running electrolyte calculations, so as not to cause acidosis or alkalosis in the patient. However, under normal conditions, you’re body can compensate for your sweat related chloride loss and keep your pH in balance.
Chloride is not available in Gatorade; it must be repleted via the diet (salty snack) or with a more dedicated oral rehydration solution (ORS) like Hydralyte, which is formulated according to the World Health Organization’s criteria for ORS’s, or Pedialyte.
Calcium and Magnesium are generally not lost in enough quantity, regarding day hiking, that ORS’s include these minerals, and would naturally be repleted via diet. Even a thru-hiker sweating 5L per day would be hard pressed to lose more calcium than what a multivitamin could provide for the day. Even the commercial backpacking foods have a certain amount of calcium, that when added to that multivitamin, would make a fair calcium intake for the day, especially after several of those meals.

Iron

There’s considerable variability as to how much iron is in exercise related sweat:

Study	Iron per L of sweat
Iron losses in sweat, Brune et al., Am J Clin Nutr. 1986 Mar;43(3):438-43	0.0225mg
Relationships between micronutrient losses in sweat and blood pressure among heat-exposed steelworkers, Tang et al., Ind Health. 2016 May; 54(3): 215–223. (Sample of 102 workers in 86-95F ambient temperature conditions)	0.283mg
Sweat iron loss of male and female runners during exercise, J J Lamanca et al., Int J Sports Med. 1988 Feb;9(1):52-5 (In this study the males sweated more than the females and the hourly loss of iron was M = 0.21mg; F = 0.276mg)	M = 0.179mg F = 0.417mg
Sweat iron and zinc losses during prolonged exercise, DeRuisseau et al., Int J Sport Nutr Exerc Metab. 2002 Dec;12(4):428-37 (hourly losses in study times averages surface area of each sex; M = 0.114mg F = 0.096mg first hour; M = 0.08mg F = 0.067mg second hour)	n/a

Iron Loss Through Sweat – various studies (mobile scroll left and right)

It also seems iron loss through sweat is diminished through longer bouts of exertion, on an hourly basis. However, even in the most extreme study result, it doesn’t appear that these losses would affect the day hiker or long distance hiker, and these marginal excretions can be repleted through diet and multi-vitamin supplementation multiple times over. Even the small amount of iron in the dehydrated backpacker’s bags is likely to be sufficient for sweat loss related repletion.

Water Soluble Vitamin Losses in Sweat During Hiking

Vitamin C (ascorbic acid)

Here’s a survey of what I can find in the literature. Lot’s of archaic studies here, but apparently, when it comes to measuring nutrient quantities in sweat, the second quarter of the last century was the golden era of discovery:

Study	Vitamin C per L of sweat
Bernstein, R. E., Nature, 140, 684 (1937)	5-11mg
Cornbleet, T., Klein, R. I., and Pace, E. R., Arch. Dermat. and Syphilol., 34, 253 (1936)	5.5-6.4mg
Wright, I. S., and MacLenathen, E., J. Lab. and Clin. Med:, 24,804 (1939)	0.24-1.86mg
Hardt, L. L., and Still, E. V., Proc. Sot. Exp. Biol. and Med., 48,704 (1941)	1.8-4.7mg
Tang, et alia, Relationships between micronutrient losses in sweat and blood pressure among heat-exposed steelworkers, Ind Health. 2016 May; 54(3): 215–223 (just the sample of men working in similar temps to hot hiking conditions, 86-95F)	2.48-5.32mg

Multiple Studies Reporting Vitamin C Levels in Sweat (mobile users scroll left and right)

Vitamin C loss through sweat and thru-hiking

I wouldn’t expect these losses to be significant with regard to day hiking, but if you’re thru-hiking the PCT and starting in Mexico during the heat, and are sweating all day long, then you could be starting to push up against your RDA’s, and should consider supplementation and/or meal planning, especially if you’re a smoker, not acclimated to the heat (after acclimation, Vitamin C in sweat falls to lower concentrations), or are a heavy sweater.

Further, the process of sweating is dependent on Vitamin C. And thus thru-hikers in high heat environments would do well to supplement their Vitamin C with a complete daily multivitamin, especially if they are depending on commercially produced dehydrated meals, that may have significantly reduced Vitamin C amounts from the dehydration process.

Lastly in higher heat environments, the skin is more susceptible to prickly heat rash, and there is evidence that preventing and treating this with Vitamin C supplementation is beneficial.

Vitamin B1 (thiamine) and Vitamin B2 (riboflavin)

Looking once more at our steel workers, we’re finding 0.045-0.089mg/L for B1, and 0.039-0.078mg/L for B2. Again not a problem if you’re a day hiker, but a one month hiking excursion for a heavy sweater, that relies on commercial dehydrated foods, who’s B vitamins may have been diminished in the preparation process, would warrant a multivitamin for the trail.

The National Research Council recommended in 1989 that thiamine consumption be 0.5mg per 1000kcals of energy intake, and since long distance hikers may be focusing on carbohydrate consumption to meet higher daily energy needs, it may be harder for them to meet thiamine needs via diet; this being further evidence that a complete daily multivitamin is a good idea. Riboflavin should be consumed at a rate of 0.6mg per 1000kcals.

Niacin and Pantothenic Acid

A few studies show that niacin shows up in sweat in small amounts: 1mg/L in the Mickelsen and Keys, 1943 study; and 0.2mg/L in the Mitchell and Edman, 1951 study. The day hiker need not worry about these small losses, but the recommendation for high temperature, high energy need exercise is 6.6mg/1000kcal of energy intake.

Again a multivitamin should be sufficient but there is some evidence (Bergstrom et al. (1969)) that taking dosage levels similar to what’s in a multivitamin, directly before exercise, may adversely effect performance (may make a 30lb pack feel heavier to a thru-hiker), by prevention of the release of fatty acids (Carlson and Oro, 1962; Williams, 1989), causing the muscle to lean heavier on muscle glycogen stores. Thus it would prudent to take in your multivitamin at the end of the day, perhaps after dinner, if you are on a multi-day hike.

The average pantothenic acid amount lost in one subject’s sweat, in the study THE EXCRETION OF ASCORBIC ACID, THIAMINE, RIBOFLAVIN, AND PANTOTHENIC ACID IN SWEAT by Tennet and Silber, 1943, was 0.074mg/L over 8 hours of sweating. This negligible amount lends no need to warrant supplementation due to sweating, either at the day hiking or thru-hiking level. Though significantly more is lost through the urine, so we’ll keep with our multivitamin theme that we have going; especially in light of the dehydrated backpacking bags, who don’t publish their water soluble vitamin content, some of us partake in.

B6 (pyridoxine) and B12 (cyanocobalamin)

Very little B6 is found in sweat. 0.007mg/L according to Mitchell and Edman, 1951. Increased heat during your hiking exertion should not pressure B6 levels downward and thus 0.016mg per gram of protein (approximately RDA levels) would be your intake goal. Same deal here: day hikers shouldn’t worry; long distance hikers, just take a complete multivitamin if you’re reliant on dehydrated food.

Like niacin, B6 has the capacity to block fatty acid production during exercise, especially in a high carbohydrate intake diet (i.e. long distance hiking), and conversely, in a low carb environment, it may accelerate depletion of glycogen in muscle during exercise. Thus the National Research Council recommends high carb exercisers do not supplement their diet with B6 past the RDA levels.

No data exists regarding high temperature stress and sweat related losses of B12. However B12 has limited absorption into the body via supplementation or diet, and those taking large doses of vitamin C on the regular could diminish that absorption further. Vegetarian/Vegan hikers likely already know that they must supplement their B12, since it is mostly found in animal products.

Interestingly enough B12 deficiency has been linked to excessive sweating, especially at night.

Fat Soluble Vitamin Losses Through Sweating

Vitamin D

There is no readily available data that shows significant Vitamin D losses via sweat, or when working/exercising in higher temperature environments. Exposure to sunlight should get you through both a day hike or a more extravagant thru-hike, but make sure you wear sunscreen either way.

Which Multivitamin Should I Take for Hiking?

In this article, I keep hammering on the idea of taking a multivitamin to supplement some of the mineral and vitamin losses, that could occur on more extravagant hiking treks (long distance hiking, thru-hiking) through sweat, at higher temperatures. Of course, in that scenario, you don’t want to be packing multiple supplements to get what you need; you just want one product that has the complete set of minerals and vitamins that could be lost through sweat or heavy exertion.

So I would stick with just a plain Centrum Adult Vitamin. Don’t get fancy with gummies that aren’t a complete multivitamin, or immune support BS that has so much zinc that you’ll be nauseous on the trail, and the only way to replete your other needs is to take that nausea inducing tablet.

Don’t forget to take the vitamin post-hike, at dinner, so some of its components don’t acutely interfere with muscle metabolism during heavy work on the trail.

Which Oral Rehydration Solution Powder Should I Take for Hiking?

Right now, I’m leaning towards NormaLyte Oral Rehydration Salts. I like this one because it doesn’t have any aspartame or sucralose in it. Plus one packet makes 500mL of solution, which is more consistent with a commercial water bottle size. Use your graduated Nalgene to figure out the right mixture of water to salt if you don’t have a commercial water bottle.

I see backpackers taking the Liquid IV brand electrolyte powders on their shorter trips, but don’t know much about that brand other than it’s expensive.