Hypertension: Could blood pressure influence sleep?

The researchers of the current study tracked the health of 66,122 women enrolled in the Nurses’ Health Study 2 (NHS2). The participants ranged in age from 25 to 42. All were without hypertension at enrollment in 2001. The researchers followed the participants’ health statuses for 16 years, assessing their blood pressure every two years. During follow-up, they observed 25,987 new cases of hypertension.

The researchers factored in lifestyle and demographic risk factors and found that women’s risk of hypertension was associated with both an insufficient amount of sleep and trouble sleeping.

Women who slept equal to or less than five hours every 24 hours were 10% more likely to develop hypertension, while women who slept six hours were 7% more likely to develop the condition.

There was no increased risk of hypertension for women sleeping more than eight hours, nor was there a greater risk for women working night shifts or having an evening chronotype.

Women who reported sometimes or usually having trouble sleeping were 14% and 28% more likely to have hypertension, respectively, compared to those who rarely had problems sleeping.

The study does not establish causality.

Dr. Nicole Weinberg, cardiologist at Providence Saint John’s Health Center in Santa Monica, California, was not involved in the study. She noted that it is difficult to figure out if sleep is causing hypertension or the other way around, or if they are related at all.

“What is it, the chicken or the egg? Like, what is the driving force here,” asked Dr. Weinberg.

Dr. Shahab Haghayegh, the study’s lead author and Harvard research fellow and biomedical engineer, suggested a possible mechanism by which sleep might promote hypertension:

“Sleep difficulties can lead to a chain of events that can increase sodium retention, arterial stiffness, and cardiac output, potentially leading to hypertension. Disruptions to the sleep/wake cycle can also influence blood vessel constriction/relaxation activity and the function of cells that regulate the vascular tone.”

A hypothesis cited in the study, on the other hand, suggests an opposite scenario in which hypertension results in poor sleep. Perhaps it causes an interruption in a 24-hour blood pressure pattern in which blood pressure drops during sleep and rises upon waking up.

Cautioning that this is just a hypothesis, Dr. Haghayegh explained: “So the difficulty in falling asleep and maintaining sleep usually occurs during the period at night when a drop in blood pressure would be expected, preventing the sleep-time dipping in blood pressure pattern.”

At the other end of sleep, this would mean an increase in blood pressure would occur upon waking. However, the researchers found no association between waking up early and hypertension.

“I should emphasize that this is purely a hypothesis, and warrants further investigation in future studies,” said Dr. Haghayegh.

The study also found that women who had insomnia or other issues with getting a good sleep had a higher body mass index (BMI), engaged in less physical activity, did not eat a high quality diet, and were more likely to smoke tobacco, drink alcohol, and be postmenopausal.

As some of these problems are also linked to high blood pressure, the mystery grows even more complex.

“High blood pressure might be an outcome of poor sleep quality/duration, or both hypertension and poor sleep might be outcomes of other underlying conditions,” said Dr. Haghayegh.

“I think what’s most interesting about the sleep issue is it’s always been a mystery: what happens while we’re sleeping,” said Dr. Weinberg.

Dr. Weinberg described, as an example, sleep interrupted by a need to urinate. “But then you put a CPAP on them, and they’re like, ‘Oddly, I didn’t have to go to the bathroom in the middle of the night.’”

“It’s not like the sensation went away,” she pointed out. “Is the sensation because there’s a blood pressure issue, or there’s some sort of flow changes in the kidneys that are activating these patients in a way that we just wouldn’t have known before because we just didn’t have the ability to get that information?”

Dr. Weinberg is ,therefore, enthusiastic about the amount of sleep-related data increasingly being made available to experts, singling out the popularity of Apple Watch’s sleep tracking.

“They’re able to figure out what’s going on when we’re sleeping in a way that we were never, ever, ever able to do before. And because of it, it’s helping us understand the disease process. I think it’s really interesting,” she said.

Dr. Haghayegh described what he thought people should take away from the study. He recommended that people “maintain vigilance in monitoring [b]lood pressure, as our findings clearly demonstrate a substantial association between poor sleep and hypertension.”

“Furthermore, regardless of the hypertension risk, individuals struggling with falling or staying asleep or obtaining sufficient sleep may benefit from exploring the underlying causes. Sleep is intricately linked to various aspects of health, and this study underscores yet another compelling reason to prioritize a restful night’s sleep.”
— Dr. Shahab Haghayegh

“It’s a push for everybody to kind of advocate for themselves. If sleep is not as refreshing as expected or is restless, you actually may say, ‘Maybe I have a sleep disorder. Maybe I should be exploring that further,’ and then your practitioner can take it from there,” added Dr. Weinberg.