What is high blood pressure (hypertension)?
Blood pressure is a measure of the force exerted by circulating blood on the walls of your arteries. This force is created by the heart as it pumps blood into the arteries and throughout the circulatory system. Blood pressure is expressed in millimeters of mercury (mm Hg) and is noted as two numbers. The first number is systolic pressure and it represents the pressure in the blood vessels when the heart beats and pumps blood out to your body. The second number is referred to as diastolic pressure. It is the pressure in the blood vessels when the heart is at rest between beats and blood is filling up with blood returning from your body [1, 2, 3].
The term normal or healthy blood pressure refers to readings of less than 120/80 mm Hg. To describe a consistently elevated blood pressure at or above 140/90 mm Hg, the term high blood pressure, also known as hypertension, is used [2, 3, 4, 5].
Thus, high blood pressure (hypertension) is an increase in the force exerted by blood flow on the arteries. It is diagnosed when the blood pressure level is 140/90 mm Hg or higher. Prolonged hypertension is a risk factor for diseases like atherosclerosis and stroke.
Rice and its nutritional values
Rice, scientifically known as Oryza sativa, is a complex grain which is made up of several components. It is a staple food for more than half of the world's population. It provides essential nutrients and energy to billions of people. Estimated more than one fifth of the calories consumed worldwide by humans [6, 7]. It is especially prevalent in East and South Asia, the Middle East, Latin America, and the West Indies [6]. Particularly in those countries rice contributes at least 20% of dietary protein and 3% of dietary fat [8].
The grain itself is composed of three parts: the bran, the germ, and the endosperm. The bran is the hard outer layer of the rice grain. It is considered the healthiest part due to its antioxidant and anti-inflammatory properties. Also, it contains bioactive components such as ferulic acid and phytic acid [9].
The germ is the reproductive part that germinates to grow into a plant. The largest part of the rice is the endosperm. This often white filling contains starchy carbohydrates, proteins, and small amounts of vitamins and minerals. However, it is important to remember that there are anatomical differences among the rice. For example, whole grain rice contains all three parts mentioned above, while white rice usually only contains the endosperm, as the bran and germ are removed during processing [9].
Rice is also a source of proteins. It contains a significant amount of prolamin, glutelin, globulin, and albumin with different solubility characteristics. These proteins exhibit a higher amino acid profile, making them nutritionally important, as when digested they give many essential amino acids [10]. The protein digestibility of rice is between 59% and 74%, with a Protein Efficiency Ratio (PER) between 1.19 and 2.31 [11].
Except for the proteins, rice is rich in micronutrients too. For example, the genetically engineered GR2E "Golden Rice". It can contribute up to 89-113% and 57-99% of the recommended daily allowance (RDA) for vitamin A for preschool children [12]. On the other hand, the rice germ, in particular, is high in iron (77% of RDA) and magnesium (108% of RDA) [13].
In some countries, like India, rice undergoes so-called fortification. During this process vitamins and minerals are added to increase its nutritional value. Fortification with iron and vitamin A can effectively increase mean haemoglobin by 1.83 and may reduce the risk of vitamin A deficiency [14].
However, it's important to note that the nutritional content of rice can be influenced by several factors. They includ agricultural practices, post-harvest processing, and the specific cultivar type [8].
Rice and high blood pressure
The connection between rice and hypertension is a complex one. It depends on many factors like the quantity and type of consumed rice, but also the overall health status of the eater and his diet. After all a healthy diet is a balanced diet.
Nevertheless, there are some indications that rice might be good for the blood pressure, especially in cases of mild hypertension. In a study, Mie Nishimura et al. gave the test group white rice enriched with gamma-aminobutyric acid (GABA). After as little as 2 weeks they found that it improved morning blood pressure in mild hypertension compared to the placebo group. The test group consumed rice with 11.2 mg GABA/100 g of rice [15]. However, the study of Mie Nishimura et al. was a small group study and was performed with fortified rice.
Another study performed by Isao Muraki et al. is a large-scale study and found no significant association between the consumption of white or brown rice and the risk of cardiovascular disease (CVD), which also includes conditions like hypertension. They compared individuals consuming ≥5 servings/week with those consuming <1 serving/week and found no significant difference in CVD risk [16]. This indicates that rice has no impact on hypertension.
A different study by Jung Tae Son and Eunjoo Lee found that reducing the amount of rice intake per meal can prevent postprandial (after eating) lower blood pressure in older people. This suggests that smaller, more frequent meals with decreased carbohydrate content, like rice, could be beneficial for managing blood pressure [17]. On the other hand, it suggests a thesis that a not reduced portion of rice could be beneficial in older people with hypertension, as it reduces the blood pressure after the meal.
On the other hand, a study by Sumathi Swaminathan et al. found that a high intake of refined grains, including white rice, was associated with a higher risk of total mortality and major cardiovascular disease events [18]. This study did not specifically focus on blood pressure, but it indicates that a patient with hypertension could increase his mortality risk, when eating large amounts of rice.
Conclusion
The question “Is rice bad for the blood pressure?” is difficult. There is no clear answer as it also depends on many factors. While some types of rice, like GABA-enriched white rice, may have beneficial effects on blood pressure, the overall impact of rice consumption on blood pressure and cardiovascular health is not easy to define. Certain is that having a high intake of any food is not the best for the health. The eating habits in life, but especially in hypertension, have to be balanced.