Blood pressure fluctuates for a variety of reasons. Even in healthy individuals, blood pressure varies due to such factors as the time of day and the level of physical activity. Additionally, such factors as salt/sodium sensitivity, stress or anxiety and hypertension, the condition of chronic high blood pressure, affect the ongoing variations in blood pressure.
Time of Day
As with many physiological functions, normal blood pressure fluctuation occurs naturally throughout the course of a 24-hour day. Typically, most people have their lowest blood pressure levels in the early morning hours, with a gradual increase by late afternoon. The typical fluctuation for most healthy individuals is about 15 points on the upper and about 10 points on the lower blood pressure readings.
In individuals with chronic hypertension, in which the blood pressure remains elevated unless treated, readings fluctuate more readily. The effect of the ongoing elevated blood pressure itself stresses the arteries. Over time, this causes the arteries to tighten up with less cause than in a non-hypertensive individual.
While the role of salt or sodium in chronic hypertension has become somewhat controversial. Some medical experts argue that the role of salt intake in hypertension has been overstated, but there are cases on record of individuals with clear salt-related effects on blood pressure. In some instances, salt-sensitive individuals can have dramatic, double-digit blood pressure increases after consuming foods containing sodium. While salt is the most well-known sodium catalyst in this regard, other sodium-containing foods can cause blood pressure fluctuations. Certain naturally salty seafoods and monosodium glutamate (MSG) can have this effect.
Stress and Anxiety
Stress or anxiety also impact blood pressure levels in most individuals. Particularly, distressing situations, as opposed to what is termed "eustress," tend to cause a rise in blood pressure. In a "eustress" situation, the affected individual can foresee a solution to the stressful circumstance and thus feels more in control through working toward that solution. In a distressing circumstance, the affected individual does not perceive a viable resolution to the stressful circumstance, which can cause anxiety and lead to an increase in blood pressure.
"White Coat Syndrome"
A variation on the stress theme, some individuals react to any doctor's visits or other medical appointments with extreme anxiety and stress levels. This is a known phenomenon that increases the blood pressure simply by virtue of being in a medical setting. True "white coat syndrome" encompasses a range of anxiety responses related to medical settings and can include elevated heart rates and shortness of breath in some individuals, among other symptoms. An alternate term for individuals who experience white coat syndrome more specifically related to elevated blood pressure is "cuff neurosis."
Level of Activity
Your level of physical activity also has a role in blood pressure variations. Most people will have lower resting blood pressure than during even sedentary activity. Regular exercise will tend to bring overall blood pressure readings down; however, in some individuals, the immediate after-effect of exercise is elevated blood pressure. For this reason, medical experts recommend against taking blood pressure readings within 20 minutes after completing an exercise session.