The study found this was independent of nutrients associated with higher intakes of fibre-rich foods including potassium and was particularly true for insoluble fibre.
The research from Imperial College London in the UK and Northwestern University in the US looked at 2195 American men and women aged between 40 and 59 as part of the INTERnational study on MAcro/micronutrients and blood Pressure (INTERMAP).
During four visits between 1996 and 1999, eight blood pressure, four 24 hour dietary recalls and two 24 hour urine samples were collected. Urinary levels of sodium, magnesium, calcium and potassium were recorded.
The results showed upping total fibre intake by 6.8 g per 4184 kilojoules (6.8 g per 1000 kilocalories) was associated with a 1.69 millimetres of mercury (mmHg) lower systolic blood pressure rating and reduced to -1.01 mmHg after adjustment for urinary potassium.
Increasing insoluble fibre intake by 4.6 g per 4184 kJ (4·6 g per 1000 kcal) was associated with a 1.81 mmHg lower systolic blood pressure - the pressure when your heart pushes blood out.
“Therefore, it may be a favourable approach to choose fibre-rich foods to prevent elevated blood pressure,” they wrote in the British Journal of Nutrition.
However soluble fibre was not associated with blood pressure.
The main dietary source of total and insoluble fibre was raw fruits (54 and 57%), followed by refined grains (16 and 14%), vegetables (15 and 12%) and whole-grain cereal products (12 and 13%).
For soluble fibre, the main dietary sources were raw fruits (48%), vegetables (21%), refined grains (19%) and whole grains and cereal products (9%).
Soluble fibre dissolves in the liquid of your stomach. It is found in foods like legumes, barley, oat bran and chia seeds. Insoluble fibre does not dissolve and instead provides ‘bulk’ and can ease defecation. It is found in foods like wheat, corn, oat bran, fruit peel, nuts and flaxseed.
They said the blood pressure-lowering effects of fibre had been attributed to a variety of factors with varying degrees of conclusiveness.
These factors included increased nitric oxide release, improved endothelial function by inhibiting sodium absorption, improved cardiovascular disease risk factors and better insulin sensitivity and hyperglycaemia.
According to the UK's National Health Service (NHS), blood pressure readings should ideally be below 120/80mmHg for the lowest possible risk of disease, however anything under 130/80mmHg is generally considered normal. Repeated readings of 140/90mmHg or higher is considered to be high.
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114515003098
“Total, insoluble and soluble dietary fibre intake in relation to blood pressure: the INTERMAP Study”
Authors: G. S. Aljuraiban, L. M. O. Griep, Q. Chan, M. L. Daviglus, Jeremiah Stamler, L. Van Horn, P. Elliott and G. S. Frost