In a blood pressure reading, diastolic pressure is the bottom number. This number describes the pressure exerted on your arteries when the heart is between beats. Low diastolic pressure can occur with or without low systolic pressure, and what is considered low diastolic pressure varies, depending on the doctor you speak with. According to MayoClinic.com, many experts say that low blood pressure (hypotension) starts at 60 and below for diastolic.
MayoClinic.com says that low blood pressure can be caused by a number of heart problems or defects. A low heart rate, also known as bradycardia, can cause a drop in blood pressure. Diastolic pressure can also be affected by heart valve problems, a heart attack or heart failure. In these situations, the heart cannot circulate the amount of blood that is needed.
MayoClinic.com also states that problems with the endocrine system can often cause low blood pressure. If the thyroid is over- or under-active, low diastolic pressure can result. Other causes include Addison's disease or adrenal insufficiency, hypoglycemia and even diabetes.
Medications and Drugs
MedlinePlus says that a number of anti-anxiety medicines, painkillers, diuretics and some antidepressants can cause the diastolic pressure to drop. Many medications used to treat high blood pressure or coronary heart disease may have the same effect.
MayoClinic.com warns that alpha blockers; beta blockers; sildenafil, or Viagra--especially when combined with the heart medication nitroglycerine--and some drugs used to treat Parkinson's disease can cause low blood pressure.
Allergic Reactions and Infections
A severe allergic reaction is known as anaphylaxis. According to MayoClinic.com, symptoms of anaphylaxis include breathing problems, itching, swollen throat and a drop in blood pressure.
MayoClinic.com also states that when an infection enters the blood stream, known as septicemia, a life-threatening drop in blood pressure can occur. This is known as septic shock.
MedlinePlus warns that dehydration can cause a drop in blood pressure. When the body is dehydrated, the blood volume drops, which can lead to a marked drop in diastolic blood pressure.
A severe lack of certain nutrients, such as vitamin B-12 or folate, has been known to cause anemia. This condition means your body does not produce an adequate number of red blood cells and low blood pressure results, according to MayoClinic.com.
For some women, pregnancy can cause low blood pressure. MayoClinic.com points out that it is common in the first 24 weeks of pregnancy for diastolic pressure to drop 10 to 15 points. This is a normal reaction, and blood pressure should return to pre-pregnancy levels after giving birth.