Why Is a Blood Test a Good Measure of Health?

By Catherine Roy, September 30, 2022

Man in short sleeves getting blood drawn

It's common to rely on subjective measures—like looking fitter, feeling better, or thinking more clearly—to evaluate your wellbeing. But those measures don’t necessarily give a full picture of your health. Bloodwork, on the other hand, shows the actual physiological response and status in the body to different interventions. 

Routine blood testing is one of the most reliable and important tools to help you evaluate and track your physical health over time. Let’s dive more into the insights of blood analysis.

What is a blood test?

A blood test is a routine lab test that looks at the different substances—or biomarkers—circulating in the blood. It's performed in a lab by a trained medical professional (doctor, nurse, phlebotomist, etc.). The sample is drawn from a vein on the inside of the arm, takes less than five minutes, and is nearly painless—just a quick pinch when the needle is inserted. Afterward, there may be some bruising, but that usually fades within a few days. 

Home blood testing kits are also available, and allow you to collect drops of blood from a finger prick. 

Why do you need multiple blood tests a. year?

What does a blood test measure?

Blood is packed with extremely informative substances like cells, proteins, hormones, nutrients, and enzymes, referred to as blood biomarkers or biomarkers for short. Levels of these biomarkers provide key insights into organ function, heart health, metabolic status, recovery, nutrition, longevity, immune function, and more. 

What are the benefits of blood testing?

Given the inherent complexities of aging, scientists have theorized for years about the exact mechanisms behind the process as they seek to understand the cause, effect, and what keeps it at bay. At one point, over 300 different theories attempted to explain the phenomenon. [7,9]

Advances in research geared towards unraveling the process have led to two prevailing categories of aging: programmed theories of aging and damage theories of aging


1. It's scientifically supported to help you meet your goals

Most trackable metrics claim to reflect the status of numerous markers of health. However, the scientific quality and validity of these various metrics are markedly different, resulting in questionable relevance of the recommendations provided. [3-5]

For example, some companies provide supplement recommendations based on questionnaire data—like how many hours of sleep you get a night or how much time you spend in the sun. Based on this data they may recommend anything from vitamin D to a probiotic. However, with just questionnaire data, how can you prove these supplements are working and are a worthwhile investment for your health?

A blood test objectively identifies key markers that are best supported by taking a supplement. For example, low levels of vitamin D. [6] Retesting after taking the supplement for a while identifies how well the supplement works and if any changes—such as increasing or decreasing that dose—are necessary. 

If there is no way to quantify if those key markers are an issue or if an intervention is even working, efforts are better put elsewhere. 


2. Blood tests are repeatable and reliable

Blood analysis is proven to be accurate and reproducibly responds to specific lifestyle modifications. [2] This means that when the same person tests their blood under the same conditions at two different time points, the results reflect a true change in the marker rather than variation associated with the testing method. 

Other measurement tools don’t offer this degree of reproducibility. For example, the estimated energy expenditure (or calories burned) from wearable devices like smartwatches are not reliable estimates and often significantly underestimate the value compared to indirect calorimetry (the gold standard). [7-10] 

If a metric is not providing you with reliable feedback, you’re likely to take a longer, more round-about path to your goals.  



3. Blood biomarkers are impacted by lifestyle 

Blood biomarkers shift in response to lifestyle factors, including food choices, supplements, exercise, recovery, sleep patterns, and stress levels. 

For example, eating oatmeal may significantly reduce LDL cholesterol, taking a curcumin supplement may improve creatine kinase, and getting at least seven hours of sleep each night helps lower hsCRP. [11-13] 

One-time tests like DNA kits have risen in popularity due to the research supporting the health benefits of diets tailored to an individual's genotype as well as interest in disease predispositions. [14,15] While these tests are useful in gaining initial insight into certain genetic traits—including having an increased, decreased, or neutral risk of unoptimized blood biomarkers—DNA does not change throughout your life, and it's not something you need to test repeatedly. 

Therefore, relying on DNA tests alone makes it difficult to discern if what you’re doing is working to your benefit.


4. It gives you relevant feedback over time 

Since biomarkers shift in response to lifestyle, and blood testing is a reliable metric, routinely testing your blood two to four times a year reveals trends in your health status. Tracking these trends allows you to proactively make adjustments before trendlines veer too far off in an unfavorable direction. Because what gets measured, gets managed. 

For example, say you’ve been taking steps to lower your elevated fasting blood glucose levels. And after consistently following a high-fiber diet and increasing cardio and weight training exercises, you have successfully decreased your fasting glucose after three months and saw even more improvement after six months. But, at the same time, you noticed your vitamin D levels have also slowly declined during that time, possibly due to less sun exposure. You may now benefit from starting a vitamin D supplement. 

Other evaluation tools that are not reproducible or have strong evidence showing an association with a lifestyle change, aren’t beneficial as long-term tracking tools. That includes stool testing. 

Stool testing claims to provide insight into the types of microorganisms living in the gut and what modifications best support gut health. However, research is still emerging on the factors that positively alter the gut microbiome and more importantly, the same test done by the same person on the same day can produce dramatically different results, let alone the differences that may occur months or even a year later. [16,17] 

If the goal is continuous improvement, the fastest way to get there is through regular check-ins and pivots based on relevant data. 


Enhance blood analysis with fitness tracking data and DNA insights

Blood provides a true measure of change in response to a modification and can be tracked over time to reveal patterns in health. Only when blood is the basis can input from other testing methods be used to further the precision and actionability of modifications geared towards meeting your goals. 

InsideTracker's proprietary analytics platform not only evaluates blood biomarkers according to your age, biological sex, ethnicity, and activity level, but it also incorporates additional insights from fitness trackers and DNA tests to give you the most holistic understanding of your health possible.



[1] Minich DM, Bland JS. Personalized lifestyle medicine: relevance for nutrition and lifestyle recommendations. ScientificWorldJournal. 2013;2013:129841. Published 2013 Jun 26

[2] Mayeux R. Biomarkers: potential uses and limitations. NeuroRx. 2004;1(2):182-188.

[3] Evenson KR, Goto MM, Furberg RD. Systematic review of the validity and reliability of consumer-wearable activity trackers. Int J Behav Nutr Phys Act. 2015;12:159. Published 2015 Dec 18. 

[4] Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J. 2017;474(11):1823-1836. Published 2017 May 16.

[5] Grimaldi KA, van Ommen B, Ordovas JM, et al. Proposed guidelines to evaluate scientific validity and evidence for genotype-based dietary advice. Genes Nutr. 2017;12:35. Published 2017 Dec 15.

[6] Żebrowska A, Sadowska-Krępa E, Stanula A, et al. The effect of vitamin D supplementation on serum total 25(OH) levels and biochemical markers of skeletal muscles in runners. J Int Soc Sports Nutr. 2020;17(1):18. Published 2020 Apr 9.

[7] Hajj-Boutros G, Landry-Duval MA, Comtois AS, Gouspillou G, Karelis AD. Wrist-worn devices for the measurement of heart rate and energy expenditure: A validation study for the Apple Watch 6, Polar Vantage V and Fitbit Sense. Published 2022 Jan 31.

[8] Evenson KR, Goto MM, Furberg RD. Systematic review of the validity and reliability of consumer-wearable activity trackers. Int J Behav Nutr Phys Act. 2015;12:159. Published 2015 Dec 18.

[9] O'Driscoll R, Turicchi J, Beaulieu K, et al. How well do activity monitors estimate energy expenditure? A systematic review and meta-analysis of the validity of current technologies. Br J Sports Med. 2020;54(6):332-340.

[10] Murakami H, Kawakami R, Nakae S, et al. Accuracy of 12 Wearable Devices for Estimating Physical Activity Energy Expenditure Using a Metabolic Chamber and the Doubly Labeled Water Method: Validation Study. JMIR Mhealth Uhealth. 2019;7(8):e13938. Published 2019 Aug 2.

[11] Yu J, Xia J, Yang C, et al. Effects of Oat Beta-Glucan Intake on Lipid Profiles in Hypercholesterolemic Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2022;14(10):2043. Published 2022 May 13.

[12] Fernández-Lázaro D, Mielgo-Ayuso J, Seco Calvo J, Córdova Martínez A, Caballero García A, Fernandez-Lazaro CI. Modulation of Exercise-Induced Muscle Damage, Inflammation, and Oxidative Markers by Curcumin Supplementation in a Physically Active Population: A Systematic Review. Nutrients. 2020;12(2):501. Published 2020 Feb 15.

[13] Morris A, Coverson D, Fike L, et al. Sleep Quality and Duration are Associated with Higher Levels of Inflammatory Biomarkers: the META-Health Study. Circulation. 2018;122(2):A17806. Published 2018 Mar 23.

[14] Nielsen DE, El-Sohemy A. A randomized trial of genetic information for personalized nutrition. Genes Nutr. 2012;7(4):559-566.

[15] Kohlmeier M, De Caterina R, Ferguson LR, et al. Guide and Position of the International Society of Nutrigenetics/Nutrigenomics on Personalized Nutrition: Part 2 - Ethics, Challenges and Endeavors of Precision Nutrition. J Nutrigenet Nutrigenomics. 2016;9(1):28-46. 

[16] Nogal B, Blumberg JB, Blander G, Jorge M. Gut Microbiota-Informed Precision Nutrition in the Generally Healthy Individual: Are We There Yet?. Curr Dev Nutr. 2021;5(9):nzab107. Published 2021 Aug 9.

[17] Zhernakova A, Kurilshikov A, Bonder MJ, et al. Population-based metagenomics analysis reveals markers for gut microbiome composition and diversity. Science. 2016;352(6285):565-569.

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