Vital signs are called vital for a reason. These basic measurements, blood pressure, heart rate, temperature, and others, provide crucial information about how your body is functioning. Understanding what they mean helps you make sense of your health and communicate effectively with healthcare providers.
Blood Pressure
Blood pressure is measured in two numbers: systolic (the top number, pressure during heartbeats) and diastolic (the bottom number, pressure between beats).
Normal: Below 120/80 mmHg
Elevated: 120-129/<80
High (Stage 1): 130-139/80-89
High (Stage 2): 140+/90+
Blood pressure varies throughout the day and is affected by stress, activity, caffeine, medications, and even body position during measurement. Single readings matter less than patterns over time.
Heart Rate
Resting heart rate is measured when you're calm and haven't been active. Normal resting heart rate for adults is typically 60-100 beats per minute. Well-conditioned athletes may have rates below 60.
What's more meaningful than any single number is your personal baseline and how it changes over time. A consistently increasing resting heart rate could signal health changes worth investigating.
Heart Rate Variability (HRV)
The variation between heartbeats, increasingly measurable with consumer devices, is associated with overall health and stress levels. Higher variability generally indicates better cardiovascular fitness and stress resilience.
Blood Oxygen (SpO2)
Blood oxygen saturation measures the percentage of hemoglobin carrying oxygen. Normal levels are typically 95-100%. Levels below 90% may indicate respiratory problems and warrant medical attention.
Many factors affect SpO2 readings: nail polish, cold fingers, dark skin (which can cause inaccurate readings on some devices), and altitude. Consistent readings below 95% should be discussed with a doctor.
Blood Sugar (Glucose)
For people with or at risk for diabetes, blood glucose monitoring provides essential information about how the body processes sugar.
Fasting glucose targets:
Normal: Under 100 mg/dL
Prediabetes: 100-125 mg/dL
Diabetes: 126+ mg/dL
For those managing diabetes, target ranges are individualized and often wider. Post-meal readings tell a different story than fasting readings, both matter.
Why Track Over Time?
A single measurement is a snapshot. Trends over days, weeks, and months reveal patterns that single readings cannot. They show whether conditions are improving, stable, or worsening, and whether treatments are working.
Body Temperature
"Normal" body temperature varies by person and time of day. The old standard of 98.6°F (37°C) is actually an average; many healthy people run slightly higher or lower. Temperature also rises in the afternoon and falls overnight.
What matters more is change from your baseline. A fever indicates your body is fighting something, even if the absolute temperature seems only moderately elevated.
Weight
Weight fluctuates daily due to fluid intake, salt consumption, bowel movements, and hormonal cycles. These short-term fluctuations are meaningless. What matters is the trend over weeks and months.
Weighing at the same time each day (typically first thing in the morning, after using the bathroom) provides the most consistent data. Weekly averages are more useful than daily numbers.
When to Be Concerned
Vital signs outside normal ranges warrant attention, but context matters:
- Blood pressure: Consistently elevated readings over multiple days
- Heart rate: Resting rates persistently above 100 or below 60 (unless you're very fit), or sudden changes
- SpO2: Readings consistently below 95%, or any reading below 90%
- Blood sugar: Readings consistently outside your target range
- Temperature: Fever above 103°F (39.4°C), or any fever lasting more than a few days
Your doctor can help interpret your numbers in the context of your overall health and conditions.
Making Tracking Work
For tracking to be useful:
- Measure at consistent times under consistent conditions
- Record the numbers so you can see trends
- Note circumstances that might affect readings (stressed, just exercised, sick)
- Share data with your healthcare provider at visits
Numbers without context are just numbers. Context makes them information.