Relation of iron and red meat intake to blood pressure: cross sectional epidemiological study
BMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a258 (Published 15 July 2008) Cite this as: BMJ 2008;337:a258
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The recent report of Tzoulaki and colleagues [1] on a large cross-
sectional epidemiological international collaborative study on macro-
/micronutrients and blood pressure (INTERMAP) indicated that blood
pressure was negatively associated with non-haem iron ingestion and
positively associated with red meat intake. Both this paper and the
accompanying editorial noted the need for confirmation of such findings
with prospective controlled studies. I am writing to draw attention to a
relevant small, but well-controlled prospective study from our laboratory.
We reported no change in the systolic or diastolic resting blood
pressure of 21 healthy premenopausal women who consumed weighed
experimental lacto-ovo-vegetarian and meat-containing diets (with
equivalent food energy) for 8 wk each in a randomized cross-over design
[2]. These two diets contained 0 and 184 g meat/d, respectively. Three-
quarters of this meat was beef, with chicken as the remainder. As
described in a subsequent paper emphasizing iron content and
absorption/bioavailability [3], the two diets contained 12.6 and 13.6 mg
total iron, and 0 and 1.2 mg haem iron/d, respectively. Compared to the
meat-containing diet, the lacto-ovo-vegetarian diet resulted in
substantially lower non-haem and total iron absorption [3]. This small
study with controlled diets for 8 wk each does not support a positive
association of red meat or haem iron intake with blood pressure, under
conditions of equivalent energy consumption.
REFERENCES
[1] Tzoulaki I, Brown IJ, Chan Q, Van Horn L, Ueshima H, Zhao L, et
al. Relation of iron and red meat intake to blood pressure: cross
sectional epidemiological study. Bmj 2008;337:a258.
[2] Hunt JR, Matthys LA, Johnson LK. Zinc absorption, mineral
balance, and blood lipids in women consuming controlled lactoovovegetarian
and omnivorous diets for 8 wk. Am J Clin Nutr 1998;67:421-430.
[3] Hunt JR, Roughead ZK. Nonheme-iron absorption, fecal ferritin
excretion, and blood indexes of iron status in women consuming controlled
lactoovovegetarian diets for 8 wk. Am J Clin Nutr 1999;69:944-52.
Competing interests:
Author has received some research funding from the National Cattlemen's Beef Association in the USA.
Competing interests: No competing interests
We have read with interest the article by Tzoulaki et al. and the
accompanying editorial. [1, 2]
Recent studies have suggested that even moderately raised iron stores
and plasma ferritin concentrations, below those seen in haemochromatosis,
may induce insulin resistance, hyperinsulinaemia, diabetes and the
metabolic syndrome. [3]
We also know that hypertension is more prevalent amongst obese
subjects or in patients with diabetes, i.e. in subjects with
hyperinsulinaemia and insulin resistance. [4] Longitudinal studies have
demostrated that insulin resistance may precede the development of frank
hypertension [5] and it is thought that the hyperinsulinaemia activates
the adrenergic nervous system. [6]
The findings of the study by Tzoulaki et al. suggest that haem iron
intake from food is positively associated with a non-statistical rise in
systolic and diastolic blood pressure. The raised haem iron intake seems
to alter iron metabolism possibly through changes in oxidative stress
leading to an increase in insulin resistance and hyperinsulinaemia
[7].Hence we hypothesise that excess haem iron intake leads to
hyperferritinaemia and hyperinsulinaemia which in turn could lead to
hypertension – our 4H-hypothesis.
REFERENCES:
[1] Tzoulaki I, Brown IJ, Chan Q, Van Horn L, Ueshima H, Zhao L,
Stamler J, Elliott P; International Collaborative Research Group on Macro-
/Micronutrients and Blood Pressure. Relation of iron and red meat intake
to blood pressure: cross sectional epidemiological study. BMJ. 2008 Jul
15; 337
[2] Stranges S, Guallar E. Dietary iron and blood pressure. BMJ. 2008
Jul 15; 337
[3] Jehn ML, Guallar E, Clark JM, Couper D, Duncan BB, Ballantyne CM,
Hoogeveen RC, Harris ZL, Pankow JS. A prospective study of plasma ferritin
level and incident diabetes: the Atherosclerosis Risk in Communities
(ARIC) Study. Am J Epidemiol. 2007 May 1; 165(9):1047-54.
[4] Ferrannini E. The phenomenon of insulin resistance: its possible
relevance to hypertensive disease. In: Laragh JH, Brenner BM, eds.
Hypertension: Pathophysiology, Diagnosis and Management, 2nd Ed. New York,
NY: Raven Press; 1995: 2281-2300.
[5] Haffner SM, Miettinen H, Gaskill SP, Stern MP. Metabolic
precursors of hypertension. The San Antonio Heart Study. Arch Intern Med.
1996 Sep 23; 156(17):1994-2001.
[6] Ferrannini E, Buzzigoli G, Bonadonna R, Giorico MA, Oleggini M,
Graziadei L, Pedrinelli R, Brandi L, Bevilacqua S. Insulin resistance in
essential hypertension. N Engl J Med. 1987 Aug 6;317(6):350-7.
[7] Jehn HL, Guallar E, Clark JM, Couper D, Duncan BB, Ballantyne CM
et al. A prospective study of plasma ferritin and level and incident
diabetes:the atherosclerosis risk in communities (ARIC) study. Am J
Epidemiol 2007; 165:1047-54
Competing interests:
None declared
Competing interests: No competing interests
Question re: type of beef used in studies
I am interested to know if any research on the relationship of beef
intake to hypertensive states has addressed the differences between
consumption of grain-fed vs. grass-fed beef i.e., does the type of fat and
protein formed by the animal's feed have any correlation to the meat's
impact on blood pressure readings.
Competing interests:
None declared
Competing interests: No competing interests