“Several studies have reported the association between hypertension and nocturia [waking up during the night to urinate], and we think that the result of our study adds evidence showing this association,” says research author Satoshi Konno, MD, with the division of hypertension at Tohoku Rosai Hospital in Sendai, Japan. “However, only a few studies have been conducted in an Asian population, which has a higher salt intake compared with Western populations.”

Study investigators collected a stream of health data on 1,882 adults (792 men and 1,102 women) from the Japanese town of Watari. The participants, who were an average of 64 years old, had received a blood pressure reading as part of an annual checkup in 2017. About 45 percent had high blood pressure, which scientists defined as having a reading of more than or equal to 140/90 millimeters of mercury (mmHg) or using anti-hypertensive drugs. Participants also answered a questionnaire, providing details on the frequency of their nighttime urination. A total of 1,295 (69 percent) reported having nocturia. About one-half of these individuals had hypertension. From this data, scientists calculated that those who urinated once or more a night were 40 percent more likely on average to have high blood pressure compared with those who did not have nighttime events. The prevalence of nocturia grew higher in proportion to systolic blood pressure levels (the top number in a reading) — 61.8 percent for those with a systolic less than 120 mmHg, 68.9 percent for those in the 120–129 mmHg range, 74.2 percent for the 130–139 mmHg range, and 74.7 percent for those 140 mmHg or higher. The researchers expected the link between high blood pressure and urination frequency would be stronger in men than women because older males can have an enlarged prostate gland (prostatic hyperplasia), which has been associated with hypertension, according to research published in the Journal of Urology. “To our surprise, nocturia was significantly associated with hypertension in both genders,” says Dr. Konno.

Salt May Increase Both Urination and Pressure

Although this investigation did not gather information on salt intake, Konno and his collaborators suspect that excessive salt consumption may play a role in frequent urination and high blood pressure. They estimate that the average daily intake of sodium for a Japanese adult is about 10 grams (g), or about 2 teaspoons — more than double the worldwide average of 4 g per day and more than 4 times the 2.3 g per day recommended by the American Heart Association (AHA). Why does the Japanese population in particular have such high sodium levels? Scientists point to a diet heavy in soy sauce–based meals and certain salty seafoods. For decades, physicians have warned that eating too much sodium can deliver a blow to heart health. Basically, consuming large amounts of salt causes the body to store additional fluid. This puts extra stress on the heart and raises blood pressure, according to the AHA. Elevated pressure in turn increases the risk of heart disease and stroke. Also, hypertension can often lead to congestive heart failure, according to Sarah Samaan MD, a cardiologist with Baylor Scott and White Legacy Heart Center in Plano, Texas. “Heart failure commonly causes nocturia, since all the excess fluid that builds up in the legs and abdomen during the day tends to move towards the center of the body when an individual is lying down,” says Dr. Samaan. “That may be one issue that contributes to this finding.” The more salt one eats, the thirstier a person gets as well. The body gets rid of excess fluids and salt through urination, according to the National Institutes of Health. So eating more salty foods can naturally lead to more bathroom expeditions. A study published in February 2019 in the journal Neurology and Urodynamics showed just that. When subjects boosted their intake from 9.9 g to 11 g, their need to urinate climbed from 2.3 times to 2.7 times per night. Conversely, average nightly bathroom trips dropped from 2.3 to 1.4 times when individuals cut their salt by a one-quarter, from 10.7 g to 8 g a day.

Shaking the Salt Habit May Improve Heart Health

The Centers for Disease Control and Prevention (CDC) estimates that 9 out of 10 Americans consume too much sodium, and about 29 percent have high blood pressure. In a study published in June 2018 in the International Journal of Epidemiology, which included about 3,000 individuals with hypertension, researchers found a direct linear relationship between increased sodium intake and increased risk of death. While reducing salt consumption may have a significant health payoff, cutting back goes beyond sprinkling less on food. Consumers need to be aware that many products contain high sodium levels. “Prepared foods, breads, soups, lunch meats, and restaurant foods are common sources of salt,” says Samaan. “Well over 75 percent of our intake comes from salt that is cooked into the food we eat, and not from the salt shaker.” Konno stresses that this study does not show any type of causal relationship between high blood pressure and frequent urination, and no details on salt consumption were obtained in this investigation. The study was limited by focusing on a population in one small geographic area. And because the information on nocturia was self-reported, it may not be accurate. Researchers next plan to investigate whether nocturia precedes the development of hypertension and how it may be influenced by salt intake. “The takeaway from this study is that one or more bathroom visits per night may be an initial sign of high blood pressure, and you should get your pressure checked,” says Konno.