Dietary supplements linked to changes in blood pressure call for further research

Changes in blood pressure can occur in people who take dietary supplements, particularly those who have a history of hypertension, new research shows. However, the study authors caution that their findings may not be causal but instead should provide a basis for further investigation of the potential for some supplements to be used for their antihypertensive properties and others to be avoided in people with high blood pressure. Using data from a large cohort study, the authors, led by Dr Catherine McCarty at the Essentia Institute of Rural Health, Duluth, Minnesota, USA, observed that small but statistically significant changes in the systolic or diastolic blood pressure were linked to a number of supplements out of 37 that were used. “A significant difference (after adjusting for age, gender, BMI and smoking) in systolic and/or diastolic blood pressure was observed between users and non-users of nine of the specific dietary supplements: coenzyme Q10, fish oil, iron, bilberry, echinacea, evening primrose oil, garlic, goldenseal and milk thistle,” the authors commented. The largest difference for systolic blood pressure was an increase of 5.3 mm Hg, (4%) in people who used evening primrose oil.  “This is a clinically meaningful difference,” they added. The study, published in the peer-reviewed journal, BMC Complementary and Alternative Medicine used the National Cancer Institute Dietary History Questionnaire (DHQ), including questions about nutritional supplement use,  issued to 18,000 living subjects (out the original 20,000) participating in a population-based biobank cohort study called the Personalized Medicine Research Project, Wisconsin, USA. Over half (mean age of 56 years, mostly female) had both blood pressure and DHQ available. Of the supplements that significantly altered blood pressure all increased either systolic, diastolic or both.  In the subgroup of people with no hypertension diagnosis, mean diastolic blood pressure was significantly lower for users of vitamin B6, cod liver oil, zinc and ginger and significantly higher for users of bilberry and goldenseal. However, most observed changes in blood pressure were small and the authors emphasised that this was a hypothesis generating study and that the relationship should not be interpreted as causal.   The study has a number of weaknesses including a lack of statistical correction for multiple comparisons, which is likely to lead to false positive associations and no investigation into the use of multiple supplements, which may have opposing effects on blood pressure. The researchers also state that the inverse associations may have resulted from altered behaviour following a hypertension diagnosis and that the questionnaires were collected after a substantial proportion (4%) of the cohort had died, introducing possible bias. High blood pressure or hypertension is defined as systolic or diastolic blood pressure ≥140/90 mmHg. According to Heart Foundation Australia, in 2012, a startling 4.6 million Australians (32%) over  18 years had high blood pressure and 3.5 million (68%) of those with  of those with high blood pressure were not taking medication.  From previous studies, there is evidence that a number of nutritional supplements significantly lower blood pressure.  Co-enzyme Q10 , fish oil and iron have consistently been associated with decreased blood pressure,  garlic has inconclusive associations and Bilberry has been associated with increased blood pressure. Also a recent meta analysis shows that levels of circulating Vitamin D (25-hydroxyvitamin D) are inversely related to blood pressure measurements in a dose dependent manner.  References 1. McCarty CA, Berg RL, Rottscheit CM, Dart RA. The use of dietary supplements and their association with blood pressure in a large Midwestern cohort. BMC Complement Altern Med. 2013 Nov 28;13:339.  2. Simons S, Wollersheim H, Thien T: A systematic review on the influence of trial quality on the effect of garlic on blood pressure. Netherland J Med 2009, 67:212-219. 3. Shim SH, Kim JM, Choi CY, Kim CY, Park KH: Ginkgo biloba extract and bilberry anthocyanins improve visual function in patients with normal tension glaucoma. J Medicinal Food 2012, 15:818-823. 4. Kunutsor SK, Apekey TA, Steur M. Vitamin D and risk of future hypertension: meta-analysis of 283,537 participants. Eur J Epidemiol. 2013 Mar;28(3):205-21.