Which is more important: systolic or diastolic pressure?

I know the topic of this question say "High Blood Pressure", but I actually have the opposite problem. Well, I wouldn't really call it a problem, but my blood pressure is normally a lot lower than the "average" healthy value.

I say it isn't a problem because I feel fine and for as long as I can tell, my blood pressure has always been low. (By low, I mean, I rarely -if ever- see triple digits).

My average blood pressure reading is about 80/60 with my heartrate about 86.  I am 23 years old and I am not on any medications. My maternal grandfather's family (I think at least all of his 10 siblings and him as well) have had some sort of heart problem including heart attacks, high blood pressure and strokes. For this reason, I am very concerned with my own health.

Today my blood pressure was a bit high (for me) at 90/53 and heartrate 89. I realize this value would still be considered "low" under normal circumstances, but since my blood pressure is normally lower than that (I've seen my systolic pressure drop below 60 at times...with no obvious symptoms) should I be concerned about today's reading?

Which value is more important over all? Should I be concerned that my systolic pressure is higher than normal, or more concerned about the much lower diastolic pressure value?

Also, since there is limited info out there about low blood pressure, can anyone tell me "how low is too low"?

Thank you.

[kenkeith]

Although blood pressure varies from person to person, a blood pressure reading of 90 or less systolic blood pressure (the top number in a blood pressure reading) or 60  or less diastolic blood pressure (the bottom number) is generally considered low blood pressure.

The causes of low blood pressure can range from dehydration to problems with the way your brain signals your heart to pump blood. Low blood pressure is treatable, but it's important to find out what's causing your condition so that it can be properly treated.

What's considered low blood pressure for you may be normal for someone else. Most doctors consider chronically low blood pressure too low only if it causes noticeable symptoms.

It can indicate a heart problem. Low blood pressure include extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure. These conditions may cause low blood pressure because they prevent your body from being able to circulate enough blood.

Endocrine problems. An underactive thyroid (hypothyroidism) or overactive thyroid (hyperthyroidism) can cause low blood pressure. In addition, other conditions, such as adrenal insufficiency (Addison's disease), low blood sugar (hypoglycemia) and, in some cases, diabetes, can trigger low blood pressure.

Dehydration. When you become dehydrated, your body loses more water than it takes in. Even mild dehydration can cause weakness, dizziness and fatigue. Fever, vomiting, severe diarrhea, overuse of diuretics and strenuous exercise can all lead to dehydration