What causes high blood pressure in young adults

My Girlfriend who is 21 years old  has been told by her doctor that she has had   high blood pressure readings for the past year (Its the bottom number that is high) . She is in good health and does not smoke. My question is how can someone at that age have high blood pressure. She is on birth controll pills can that be a factor?

   Her doctor has taken blood samples from her and sent then to a speciallist.

[CCF CARDIO MD JMF]

Dear Andrew,

Birth control pills may do this as can extra weight or this may be essential hypertension ( Hypertension that is genetic).  

It is also important to rule out renal artery stenosis if her levels have shot up recently or are particularly difficulat to control with medication.

[baseballmom1227]

A related discussion, blood pressure was started.

[Rachelmek]

I suffer from what is called Polycystic Kidney Disease (google it) which causes chronic kidney stones. Many people have this disease with no signs until they are much older. When their kidneys begin to fail them. The main symptom is high blood pressure beginning as a young adult. why? Because your kidneys are working too hard fighting off the cysts and they are not filtering correctly. I was diagnosed with PKD in July last year after a car accident. I just happened to decide to see a friend who happened to also be a urologist as I did not have medical insurance and knew he would let me pay it out.  He ran a series of tests and came to find I had chronic kidney stones. A total of 6. Just in there. Probably been there for years. If you have high blood pressure on top of chronic stones I highly recommend you get tested. A CT scan is the best way to get diagnosed and make sure you see a Urologist who. If you would like to here more about my story I will happily tell you. Before you get tested you need to know this is a fatal disease and this will affect your ability to get life insurance and affordable health care if you do not have it prior.