Urea is an important measure of our kidney health, liver health, and protein turnover. A urea blood test is often ordered as a part of a comprehensive metabolic panel, which gives a broad overview of a person’s metabolic and overall health. Continue reading to discover more about urea and what high or low levels mean for your health.

What is Urea?

Urea is a waste product that the liver makes when it degrades protein. Protein is mostly derived from the diet, but can also result from tissue protein turnover [1, 2, 3].

On a normal/average diet, we produce about 12 g of urea each day [3]. The bulk of it, about 10 g each day, is eliminated by the kidneys [3].

A small amount of urea (less than 0.5 g/day) is lost through the gut, lungs, and skin. During exercise, a substantial amount may be lost through sweat [3].

Blood urea levels represent the balance between urea production (in the liver), urea breakdown, and urea elimination/removal (by the kidneys) [4].

Therefore, urea is a useful indicator of kidney health and/or liver health. It is also used to check for severe dehydration.

Urea Test

The urea test is often ordered for people who are experiencing signs and symptoms of kidney disorders. These symptoms can include:

  • Frequent urination
  • Discolored urine (bloody, dark, or foamy)
  • Joint pain
  • Bone pain
  • Back pain
  • Muscle cramping
  • Restless legs
  • Fatigue
  • Trouble sleeping
  • Poor appetite
  • Swelling (especially in the extremities)
  • Itchiness

Urea Normal Range

In Europe, the whole urea molecule is measuredNormal human blood should contain between 1.8 – 7.1 mmol/L.

In the United States only the nitrogen component of urea is measured (the blood urea nitrogen, i.e., BUN), which is roughly one-half of blood urea [1]. The normal range for BUN is between 5 – 20 mg/dL.

To convert from mmol/L into mg/dL, divide by 0.357.

The range is wide because there are many factors that affect blood urea levels [1]:

  • the amount of protein in the diet
  • protein breakdown
  • state of hydration
  • liver urea production
  • urea elimination by the kidneys

Urea can both decrease and/or increase in pregnancy [5, 6].

Low Urea Levels

Low urea levels are often not of great concern. However, in some cases, they point to underlying issues:

  • Low-protein diet, malnutrition, or starvation [3]
  • Impaired liver activity due to liver disease, often linked to alcohol abuse [3, 7]
  • Overuse of anabolic steroids, which decrease protein breakdown [8]
  • Overhydration, or drinking too much water [7]
  • Growth hormone use. Growth hormone-deficient children given human growth hormone have lower urea, and this is due to decreased urea production [9, 10]
  • Genetic deficiency of urea cycle enzymes [3]

Urea can be decreased in pregnancy [5].

How to Increase your Urea Levels

Low urea levels can mean that you are not consuming enough protein. If this is the case, try to increase your consumption of protein-rich foods like lean meats or beans [1].

Reduce alcohol consumption. Alcohol blocks the production of urea [11].

High Urea Levels

High urea levels can result from serious underlying health conditions and diseases. In addition, elevated urea is bad in its own right.

High urea levels increase oxidative stress in cells [12, 13].

High urea means there is increased protein breakdown, which is associated with decreased immune function. In a study of 26k patients, those with elevated urea had an increased risk of infection and a higher risk of dying [4].

High urea is associated with increased mortality in ill patients in four studies with over 28k patients) [4, 14, 15, 16].

Elevated urea is also associated with increased stroke risk in heart surgery (5498 subjects), and adverse outcomes in atherosclerosis (1521 subjects) and heart failure patients (225 patients) [17, 18, 19].

Blood urea levels increase as we age [20].

Levels can also rise in pregnancy [6].

Causes of high urea levels include:

  • Dehydration/low water consumption – Urea increases as blood volume decreases [4]
  • High protein diets [3]
  • Fever or infection, which increases protein breakdown. Increased protein breakdown is a common feature of illness. Protein breakdown is stimulated by hormones (such as glucagon, epinephrine, and cortisol) and inflammatory cytokines. Protein production, on the other hand, is reduced by lowering growth hormone, insulin, and testosterone levels [3, 4]
  • Inflammation or interval training, which results in protein breakdown from muscle
  • Stress – An inappropriate increase in the activation of the sympathetic, renin-angiotensin-aldosterone, and vasopressin systems elevate BUN, which is often seen in heart failure. Cortisol will also increase protein breakdown and elevate BUN [21, 22]
  • Gut bleeding – When upper GI bleeding occurs, the blood is digested to protein. This protein is transported to the liver and metabolized to BUN [3, 2]
  • Poor circulation, which results in lower blood flow to the kidneys and therefore less of an ability to clear the urea [23, 4]
  • Thyroid issues, which result in abnormal kidney function: hypothyroidism, and hyperthyroidism [24, 25]
  • Anti-anabolic drugs such as glucocorticoids and tetracyclines (except doxycycline) [3]
  • Lower growth hormone or IGF-1. IGF-1 and growth hormone inhibit urea synthesis [10]
  • Kidney disease or failure, and blockage of the urinary tract by a kidney stone [6]
  • Inborn errors of metabolism (genetic urea cycle disorders) [13]

How to Decrease your Urea Levels

There are two easy ways to decrease your blood urea levels:

  • Drink more water (stay properly hydrated)
  • Eat less protein

Also, try losing weight if overweight. Because a high BMI can cause kidney dysfunction, weight loss can help improve kidney health and lower urea levels [26, 27, 28].

Supplements that can help decrease urea:

  • Ginger may help remove urea from the blood. Ginger extract markedly decreased BUN in mice [29].
  • Pomegranate [30]
  • Flaxseed oil (may protect the kidneys, decreases BUN) [31, 32]
  • D-ribose [33, 34]
  • Ashwagandha [35, 36]
  • Curcumin [37]

Irregular Urea Levels?

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