To our knowledge, this is the first study focused on the prevalence of hypertension among travelers in Thailand. In our study, the overall prevalence of hypertension was 28.84%. Interestingly, this prevalence was much higher than other reports. A previous study from a travel clinic in Marseille, France, reported a prevalence of 4.6%, while a study from Galway, Ireland revealed a self-reported prevalence of 2.9% [10, 15]. The high prevalence of hypertension in our study may be a result of including both individuals with pre-existing hypertension, and newly diagnosed hypertension. while most previous studies included travelers with pre-existing hypertension only [10, 15].

It is reasonable to suggest that the prevalence of newly diagnosed hypertension in our study was overestimated due to the “White Coat Hypertension” phenomenon. This phenomenon is characterized by an elevated blood pressure reading in a medical facility, while the individual’s ambulatory blood pressure remains within the normal range [16]. Moreover, although we complied with standard blood pressure measurement guidelines (two measurements with adequate rest) and standard criteria to diagnose hypertension, we used a single clinic visit to diagnose hypertension. Several studies suggest that single clinic visits tended to overestimate the prevalence of hypertension [17,18,19,20]. A large study in China showed that the prevalence of hypertension at one visit was 18.1%, however this dropped to 9.47% following a second visit [19]. Another study from Switzerland showed a similar result which reported that the prevalence of hypertension between one and two visits decreased by 13% (from 33.8 to 29.5) [20].

Although the prevalence of newly diagnosed hypertension in our study (22.15%) was likely to be overestimated, we could not totally ignore this prevalence. If we assume the effect of a single clinic visit and white coat hypertension was around 50% overestimated, at a conservative estimate, we can still observe an 11% prevalence of newly diagnosed hypertension in our group (mean age 38.5 years). This value is comparable to the prevalence in the general population in the same age group. Recent reports from the National Center for Health Statistics, United States showed that people aged 18–39 years had a 22.4% prevalence of hypertension [21], while a survey in Thailand reported a 17% prevalence of hypertension in the 30–44 year age group [22]. These findings indicate that travelers should undergo screening for undiagnosed hypertension.

It is also important to note that, according to the World Health Organization, up to 46% of adults with hypertension are unaware that they have the condition, as healthy individuals may not have their blood pressure measured for many years [23]. Travel medicine practitioners have an opportunity to detect this common medical problem when they see travelers during a pre-travel consultation. Vital signs including blood pressure should be evaluated in all travel clinic visits as a basic standard. The findings from this study suggest that DLP and DM should be evaluated in travelers with pre-existing hypertension.

The prevalence of travelers with pre-existing hypertension in our study was 6.7%. Our prevalence was higher when compared to that reported from France (4.6%) and Ireland (2.9%) [10, 15]. One possible explanation for this discrepancy could be the age difference between the populations studied. It is well known that the prevalence of hypertension increases with age. In our study, the average age among travelers was 37.1 years, while the average ages among travelers in the French and Irish studies were 31.7 and 36.6 years, respectively. Other reports also show a similar trend, such as another French study which reported a prevalence of hypertension of 25.3% among Hajj pilgrims (average age 58 years) [24].

Among the 11 participants that agreed to participate in the blood pressure monitoring arm of the study, we found that most of them had well controlled blood pressure before and during the trip. There was no significant change in SBP, DBP, MAP throughout the trip. Although their blood pressure in the morning was slightly higher than in the evening, this was not clinically relevant (less than 10 mmHg). This finding may be due to the phenomenon known as the “morning surge of blood pressure”. This has been documented in various reviews as a normal aspect of human physiology due to the effect of circadian rhythm, which can cause high blood pressure levels in the morning [25, 26]. Another factor that might have led to higher blood pressure in the morning was the medications taken, since most travelers measure their blood pressure before taking their antihypertensive medication. It is well known that anti-hypertensive medication might take several hours to reach its maximum effect, and this might be the reason why blood pressure readings seem to be more favorable in the morning. However, with modern antihypertensive medication with longer half lives (once daily dosing), the effect of timing would be much less significant. Another aspect to consider that may have impacted data accuracy is the use of different mobile automated blood pressure devices for each participant, which made it difficult to calibrate the devices and maintain consistency in measurements.

Although it is reasonable to assume that during international travel, travelers might have difficulty controlling their blood pressure due to several reasons, we could not demonstrate that in our study. Over 90% (10/11) travelers had stable blood pressure control during the trip, while only one participant had clinically insignificant higher blood pressure (≥ 10 mmHg). Moreover, all participants remained well, and no hypertension-related clinical events were reported during the trip.

Nevertheless, it is important to keep in mind that international travel can be stressful due to a variety of reasons including airport stress, lack of sleep, jet lag, and language/communication barriers, all of which can negatively impact blood pressure control. Dietary habits may also adversely impact blood pressure regulations, especially when consuming foods and beverages high in salt, caffeine, and alcohol. Those factors can contribute to an increase in blood pressure levels [14, 27, 28].

Travelers with pre-existing hypertension should have their blood pressure under control before the trip and continue taking their own antihypertensive drug(s) throughout the trip. Failure to take medication is always the main reason that makes blood pressure uncontrollable. Severely high BP or marked variation of blood pressure during the trip can lead to serious or even fatal consequences.

There are several limitations to this study. Firstly, newly diagnosed cases of hypertension were determined based on high blood pressure readings taken at two separate timepoints within a single visit, which may lead to overestimation when compared to using multiple measurements over several visits or using ambulatory blood pressure monitoring. Secondly, participants enrolled in the second arm of the study were a unique group with well-controlled blood pressure before the trip, very good compliance with their doctor’s advice, and use of their own blood pressure measurement device. The results relating to blood pressure stability during the trip in this group might not, therefore, be generalisable to other hypertensive travelers.