Summer can shake-up your usual routine. Suddenly you’re juggling kids on school break, eating dinners on the back porch, and sweating buckets during workouts. 

As the temperature rises, it’s also common to eat different foods, drink more alcohol, and go to bed later. 

All of these changes affect your health. As your habits and rituals shift into summer mode, your body will too. Even if your routine remains the same, heat, humidity, and sunshine can affect your biology. 

You can see these changes directly with a blood test. 

During summer, many of your biomarkers—the proteins, minerals, and other compounds that show how your body is working—will likely rise or fall.

"Yes—summer affects our biomarkers," says Stacey McIlroy, MMS, PA-C, assistant professor of physician assistant studies at Keck Graduate Institute.¹ But “timing, context, and environmental exposure all matter."

» Click to learn more about routine blood testing 

If you’re taking an InsideTracker blood test this summer—or if you’re simply looking to understand how the seasons affect your health—keep reading. 

By learning how your body responds to summer, you’ll be better equipped to keep your health optimized. 

Inflammaton markers
Monocytes and Lymphocytes

Hot weather can trigger an inflammatory response in your body. This is especially true during strenuous exercise or long days at the beach.² 

“Even brief exposure to high temperatures may impair immune defenses," says McIlroy.

You can see this in your blood. Research shows that monocytes and lymphocytes, white blood cells that defend your body, can rise after even short-term heat exposure.³ 

“An acute rise [after exercise in the heat] would be completely expected,” says Shawn M. Arent, PhD, professor and chair of the Department of Exercise Science at the University of South Carolina.⁴  “Chronic elevations mean we need to take a closer look.”

When inflammation is elevated over days, weeks, and months, it can damage healthy tissues and put strain on the heart.⁵

Stay optimized
Balance your exercise and heat exposure with hydration, rest, and recovery. This will let your inflammation biomarkers fall back to healthy levels. 

If you can, avoid high-intensity workouts during peak heat and humidity. And be aware of excessive heat in your workplace or home.⁶ 

Finally, steer clear of strenuous activities for two days before any blood tests. This will help prevent temporarily elevated biomarkers from skewing your results.

Electrolytes
Sodium, potassium, calcium, and magnesium

When you sweat—whether from exercise, heat, or humidity—you lose essential minerals called electrolytes. These include sodium, potassium, magnesium, and calcium. And the more you sweat, the more you lose. 

Electrolytes are important for muscle function, hydration, and nerve signaling.⁷ A drop in these markers can leave you feeling sluggish, crampy, or lightheaded.⁸ 

Low electrolyte levels can also lead to a host of symptoms such as muscle spasms, headaches, dizziness, or fatigue. 

If you’re unsure whether your electrolytes are within the optimal range, consider booking a blood test.

Stay optimized
For moderate activity, water is usually enough. But if you’re sweating heavily, especially during longer workouts or hot days, consider drinking electrolyte-rich beverages.⁹ 

“If you're sweating a lot and only replacing fluids with water, you're not replenishing electrolytes,” says Arent. That can affect your performance and increase your risk of heat stroke. 

For general hydration, don’t forget to monitor your urine color—it should be pale yellow, not dark.

» Hydration, Sodium, Potassium and Exercise: What You Need to Know

Sleep markers
Duration, REM, and deep sleep

These aren’t blood biomarkers, but they are critical health markers. They can affect nearly every aspect of your mind and body, which is why InsideTracker monitors and analyzes them alongside your DNA and blood data.

Unfortunately, many people struggle to get good sleep during the summer. That’s when sleep duration, REM sleep, and deep sleep tend to suffer. There are three notable reasons for this:

1) Longer daylight hours encourage people to go to sleep later and wake up earlier.¹⁰ 

2) Warmer nighttime temperatures, especially in homes without air conditioning, can make it harder to fall into deep, restorative sleep.

3) People are often busier with travel and weekend and evening plans. 

Stay optimized
Create a sleep-friendly environment by keeping your bedroom cool, dark, and quiet. 

Even small changes in room temperature or light exposure can lead to reduced REM and deep sleep, which are crucial for recovery and hormonal balance.¹¹

Research shows the optimal temperature for sleep is between 60 and 67 degrees Fahrenheit.¹² For light and sound, blackout curtains, fans, and white noise machines can all help. 

Finally, stick to a consistent sleep schedule, even if summer activities tempt you to stay up later. A regular sleep routine will help your circadian rhythm align itself with your needs.

The sunshine vitamin
Vitamin D

Older adults and those with darker skin tones naturally produce less vitamin D from sun exposure, and sunscreen use can further limit synthesis.

Stay optimized
Most healthy adults need 600 to 800 UIs of vitamin D each day to avoid a deficiency, which can lead to osteoporosis and risk of broken bones.¹⁶

Cholesterol markers
LDL, HDL, and total cholesterol

Stay optimized
Heart disease is the leading cause of death in the U.S. and worldwide. It should be a year-round goal to keep your heart-health biomarkers optimized. 

To do that, you should start with at least 30 minutes of exercise most days of the week. If you smoke, stop. Avoid drinking too much. And for diet, focus on whole foods like fruits, vegetables, and lean protein.²² 

» Why You Should Care About Heart Health—and 6 Ways to Optimize It

Your blood test might show these biomarkers changing in the summer, but that doesn’t necessarily signal a problem.

Red blood cell indicators
Hematocrit and hemoglobin

Don’t fret if you see these biomarkers fall a bit. This is normal during summer. 

In response to heat and exercise, your body expands plasma volume—the fluid portion of your blood.²³ This helps regulate core temperature and improves circulation.

This expansion can dilute red blood cell markers like hematocrit and hemoglobin, making them appear lower on blood tests.²⁴

“Low red blood cell markers can indicate anemia, but in this case, it’s a “false flag,” says Arent. “It’s not true anemia. It just looks that way because of plasma volume expansion, which is actually one of the best adaptations we get in the heat.” 

This phenomenon is sometimes referred to as “athletic anemia”—a harmless shift in values due to training and environmental conditions.²⁵

Stay optimized
Don’t be alarmed by a small seasonal dip in hemoglobin or hematocrit, especially if you're well-hydrated and training consistently. “Over time, this tends to renormalize,” says Arent. 

For the best insight into your health, track your red blood cell indicators over time to see how they rise and fall with the seasons. (This is why InsideTracker is built for long-term tracking—so you can focus on trends rather than individual data points.)  




Schedule a blood test today

If you want to get a handle on your health, now’s the perfect time. 

With InsideTracker, you’ll learn how your body responds to heat, humidity, and all the other changes that come with summer. 

With long-term tracking, you’ll build an intuition about what’s happening inside your body. And with personalized recommendations, you’ll know which foods, exercises, and lifestyle habits to focus on during every season. 

References: 

1) https://www.kgi.edu/people/stacey-mcilroy.html
2) https://pubmed.ncbi.nlm.nih.gov/16061150/
3) https://newsroom.heart.org/news/heat-exposure-may-increase-inflammation-and-impair-the-immune-system
4) https://sc.edu/study/colleges_schools/public_health/faculty-staff/arent_shawn.php
5) https://newsroom.heart.org/news/heat-exposure-may-increase-inflammation-and-impair-the-immune-system
6) https://www.hopkinsmedicine.org/health/conditions-and-diseases/exerciserelated-heat-exhaustion
7) https://www.heart.org/en/news/2024/06/19/electrolytes-can-give-the-body-a-charge-but-try-not-to-overdo-it
8) https://my.clevelandclinic.org/health/symptoms/24019-electrolyte-imbalance
9) https://www.heart.org/en/news/2024/06/19/electrolytes-can-give-the-body-a-charge-but-try-not-to-overdo-it
10) https://pmc.ncbi.nlm.nih.gov/articles/PMC8080821/
11) https://pmc.ncbi.nlm.nih.gov/articles/PMC3427038
12) https://health.clevelandclinic.org/what-is-the-ideal-sleeping-temperature-for-my-bedroom
13) https://pmc.ncbi.nlm.nih.gov/articles/PMC3897598/
14) https://www.epa.gov/sites/default/files/documents/uviguide.pdf
15) https://pmc.ncbi.nlm.nih.gov/articles/PMC10239563/
16) https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#en1
17) https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
18) https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
19) https://www.health.harvard.edu/staying-healthy/taking-too-much-vitamin-d-can-cloud-its-benefits-and-create-health-risks
20) https://www.sciencedaily.com/releases/2014/03/140327100804.htm
21) https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/symptoms-causes/syc-20350800
22) https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/symptoms-causes/syc-20350800
23) https://pmc.ncbi.nlm.nih.gov/articles/PMC2963322/
24) https://ui.adsabs.harvard.edu/abs/2021IzAOP..57.1271K/abstract
25) https://www.gssiweb.org/en-ca/article/sse-81-anemia-and-blood-boosting