At baseline in 1991, the mean age of the population was 36 years (standard deviation, 4.6 years), and the mean BMI was 23.7 kg/m2 (standard deviation, 4.3 kg/m2). During 14 years of follow-up, 12,319 women reported a new diagnosis of hypertension (approximately 15% of the population).
The multivariable-adjusted associations between the 6 individual modifiable risk factors and incident hypertension are shown in . The strongest risk factor was a higher BMI, with obese women having a HR for incident hypertension of 4.70 (95% CI, 4.45-4.96) compared with women whose BMI was <23.0 kg/m2. In this population, 40% of new hypertension cases (95% CI, 38-41%) could hypothetically be attributed to overweight or obesity (defined as a BMI ≥25 kg/m2), and 50% of new cases could hypothetically be attributed to a BMI ≥23.0 (95% CI, 49-52%). The other 5 modifiable risk factors were also associated with incident hypertension after multivariable adjustment (). The other modifiable risk factors were associated with individual hypothetical PARs much lower than overweight and obesity: 17% (95% CI, 15-19%) for routine analgesic use, 14% (95% CI, 10-17%) for not following a DASH style diet, 14% (95% CI, 9-19%) for not engaging in daily vigorous exercise, 10% (95% CI, 8-12%) for no or excessive alcohol consumption, and 4% (95% CI, 1-7%) for folic acid supplement use <400 μg/d.
Distribution of Modifiable Risk Factors and Multivariable Hazard Ratio of Hypertension among 83,882 Young Women in the Nurses’ Health Study II, 1991-2005.
Specific groups of 3, 4, 5, and 6 low-risk factors were associated with progressively lower HRs of developing hypertension in multivariable models (). Women with a combination of normal BMI (<25 kg/m2), daily vigorous physical activity, and a DASH type diet (in the highest quintile of DASH score) had a HR for incident hypertension of 0.46 (95% CI, 0.39-0.54). The hypothetical population attributable risk was 53% (95% CI, 45-60%), suggesting that 53% of new onset hypertension in this population might potentially have been prevented if all women had these 3 low-risk factors. The corresponding hypothesized ARD was 6.02 cases/1000 py, and the hypothesized NNT over 10 years was 16.6 women. The hypothetical PAR increased to 58% (95% CI, 46-67%; ARD=6.28 cases/1000 py, NNT over 10 years=15.9) if the low-risk group also included modest alcohol intake (in addition to normal BMI, daily exercise, and DASH type diet), and to 72% (95% CI, 57-82%; ARD=7.76 cases/1000 py, NNT over 10 years=12.9) if women also avoided routine analgesic use. Only 0.3% of the population had all 6 low-risk factors (including use of ≥400 μg/day of folic acid supplementation), but the analysis of hypothetical PAR suggested that if all women were low-risk for all 6 factors, then 78% (95% CI, 49-90%; ARD=8.37 cases/1000 py, NNT over 10 years=11.9) of new-onset hypertension might potentially have been avoided.
Multivariable Relative and Hypothesized Population Attributable Risks of Incident Hypertension among 83,882 Young Women with Different Constellations of Low Risk Factors.
The association between a parental family history of hypertension and the development of hypertension in the child may represent the effect of both genetic and non-genetic factors.34
To address whether a low-risk lifestyle would be similarly associated with lower hypertension risk among those with and without a familial predisposition to developing hypertension, we repeated our analyses after stratifying by family history of hypertension (). The hypothetical PARs associated with the constellation of 3 low-risk factors was 57% (95% CI, 43-67%; ARD=4.60 cases/1000 py, NNT over 10 years = 21.7) among women without a family history of hypertension, and 51% (95% CI, 40-60%; ARD=7.66 cases/1000 py, NNT over 10 years=13.1) among women with a positive family history of hypertension. Among women without a family history of hypertension, the hypothetical PAR was 90% (95% CI, 32-99%; ARD=6.82 cases/1000 py, NNT over 10 years=14.7) in women who lacked 6 low-risk factors; a similar analysis among women with a family history of hypertension yielded a hypothetical PAR of 69% (95% CI, 25-87%; ARD=9.87 cases/1000 py, NNT over 10 years=10.1). Tests for interaction were null regardless of which constellation of low-risk factors was considered.
Multivariable Relative and Hypothesized Population Attributable Risks of Incident Hypertension among 83,882 Young Women with Multiple Low Risk Factors and Stratified by Family History of Hypertension.
Oral contraceptive use at some point during follow-up was common (85.7% of women) and was independently associated with an increased risk of incident hypertension; OC use may potentially have contributed to 15% of all new cases of incident hypertension (95% CI, 11-20%). We addressed whether the association of various constellations of low-risk factors differed among those women who did vs. did not use OC (), with OC use updated with each questionnaire cycle as a time-dependent variable. Among non-OC users, the hypothetical population attributable risks ranged from 59% (95% CI, 48-69%) for 3 low-risk factors to 83% (95% CI, 30-96%) for the 6 low-risk factors. Among OC users, the hypothetical population attributable risks ranged from 48% (95% CI, 35-57%) to 73% (95% CI, 28-90%). Again, we found no evidence for effect modification.
Multivariable Relative and Hypothesized Population Attributable Risks of Incident Hypertension among 83,882 Young Women with Multiple Low Risk Factors and Stratified by Oral Contraceptive Hormone Use.
Because BMI was by far the strongest risk factor for incident hypertension, we examined whether a low-risk lifestyle had similar hypothetical PARs depending upon whether women were normal weight, overweight, or obese (). Overall, we found that constellations of low-risk factors were inversely associated with hypertension among normal weight and overweight women, but not among obese women (p-interaction = 0.02). Specifically, among normal weight individuals (BMI<25 kg/m2), a constellation of 4 low-risk factors (DASH type diet, daily exercise, modest alcohol intake, and avoidance of analgesics) was associated with a HR for incident hypertension of 0.46 (95% CI, 0.30-0.71); the corresponding hypothetical PAR was 54% (95% CI, 29-70%; ARD=3.19 cases/1000 py, NNT over 10 years=31.3). This same constellation of low-risk factors among overweight women (BMI 25.0-29.9 kg/m2) yielded a hypothetical PAR of 47% (95% CI, 4-71%; ARD=6.83 cases/1000 py, NNT over 10 years=14.6); however, among obese women, the hypothetical PAR was a non-significant 5% (95% CI, 0-51%). We also tested a constellation of 5 low-risk factors (DASH type diet, daily exercise, modest alcohol intake, avoidance of analgesics, and use of ≥400 μg/day of supplemental folic acid) among normal, overweight, and obese women, and found that the hypothetical PAR if women lacked these low-risk factors was 62% (95% CI, 14-83%, ARD=3.65 cases/1000 py, NNT over 10 years=27.4) among normal weight women, and not statistically significant among overweight and obese women, albeit the sample sizes were very small ().
Multivariable Relative and Hypothesized Population Attributable Risks of Incident Hypertension among 83,882 Young Women with Multiple Low Risk Factors and Stratified by Body Mass Index.
Baseline mean blood pressures and end-of-follow-up blood pressures and anti-hypertensive medication use among all women (including those who did and did not develop hypertension during follow-up) are shown in . In 2005, mean systolic and diastolic blood pressure was lower by 4/3 mmHg for those with 3 low-risk factors up to 6/4 mmHg for those with 6 low-risk factors (p<0.001 for both comparisons). Additionally, anti-hypertensive medication use was lower among those with low-risk factors. Of the women with 3 low-risk factors, anti-hypertensive medication use at the end of follow-up in 2005 was 5.8% compared to 11.7% among those who did not have these low-risk factors (p<0.001). For 6 low-risk factors, this comparison was 3.9% vs. 11.9% (p<0.001).
Blood Pressures and Anti-Hypertensive Medication Use at Baseline and End of Follow-up in all study participants, including those who developed hypertension.