Every year, the NHS needs 135,000 new blood donors to ensure that there is enough, covering all blood groups. The health service needs 5,000 donations a day. Even in normal times, that’s a tall order. In this blog we look at why blood is so precious, and provide some dietary tips to help support this “liquid” organ.

When is a blood transfusion necessary?

A healthy body replaces minor blood losses through the increased production of new blood. If the blood loss is significant, however, the body is unable to keep up. This can be the case, for example, after blood loss due to an injury or during surgery. A prolonged (chronic) blood loss can also make a blood transfusion necessary. This is the case with some cancers or blood formation disorders such as leukaemia. Whether a blood transfusion is required depends not only on the amount of blood lost, but also on the patient’s state of health. For example, people with heart disease tend to run into problems more easily after blood loss.

What does blood do?

Even without knowing the details, humans must have known that there can be no life without blood since evolution. Bleeding is bad news, and losing copious amounts of blood means certain death. Nonetheless, bloodletting was used to cure or prevent diseases for thousands of years. Although it was more likely to exacerbate a patient’s condition, the practice wasn’t debunked until the 19th century.

So, we know that we need blood … but why? What does it do?

Blood is thicker than water (literally!) and feels somewhat sticky. The temperature of blood is about 38°C, which is about one degree more than body temperature. The amount of blood depends mainly on a person’s height and weight. A man weighing about 70 kg has about 5 to 6 litres of blood in his body.

The blood consists of about 55% blood plasma and about 45% various blood cells. Blood plasma is a light yellow, slightly cloudy liquid and is more than 90% water. Most of the remaining 10% are proteins, but blood plasma also contains hormones, electrolytes (minerals), vitamins and other nutrients such as glucose and amino acids. More than 99% of the solid components of blood are red blood cells (erythrocytes). The pale or colourless white blood cells (leukocytes) and blood platelets (thrombocytes) represent the remaining 1%.

The blood has three essential tasks in the body: transport, regulation, and protection.

It carries oxygen from the lungs to the body’s cells, where oxygen is needed for metabolism. The waste product created during metabolism, carbon dioxide, is returned to the lungs via the blood and then exhaled. Apart from oxygen, the blood also supplies the cells with nutrients and hormones and disposes of other waste products that are then excreted via the liver, kidneys, or intestines. Of course, blood also serves to transport injected medicinal or recreational drugs to their target cells.

Body temperature is regulated via the blood. Blood plasma can absorb or release heat. The temperature is also dependent on the speed of the blood flow. When blood vessels dilate, the blood flows more slowly, and this favours the release of heat. If the ambient temperature is low, the blood vessels can constrict to release as little heat as possible.

Solid blood components such as platelets and some substances dissolved in the blood plasma are involved in the protective role of blood. If a blood vessel is injured, they clump together and ensure, for example, that a minor wound soon stops bleeding. This protects the body from blood loss.

Lastly, blood forms an indispensable part of the immune system. The different types of blood cells have different tasks: Some fend off microbial invaders and render them harmless. Others produce antibodies that are specifically directed against foreign substances or pathogens such as viruses. In addition, leukocytes play a role in allergic reactions. A type of lymphocytes called natural killer cells destroy damaged and malfunctioning cells before they can grow into a tumour. Without them, we would get cancer a lot more often than we do.

The blood is contained and circulated within the cardiovascular system: blood vessels, heart and lungs. A while ago, we shared our three top tips for a healthy heart. Our next newsletter will contain more tips on how to keep your cardiovascular system ship-shape with food. It’s not too late to sign-up – just enter your email in the box at the bottom of our home page.

Three facts you might not know about blood

Blood gets its colour from the red blood cells, which are red because they contain the oxygen-carrying protein haemoglobin. Haemoglobin is a molecule that has iron at its centre, and it’s the iron that makes haemoglobin and thus blood red. The blood of spiders, snails and lobsters is blue because instead of haemoglobin, they have haemocyanin, which has copper at its centre. Chlorophyll, the pigment that makes plants appear green, is also very similar to haemoglobin. The only difference is that it contains magnesium instead of iron.

There are eight main blood types: A positive, A negative, B positive, B negative, AB positive, AB negative, O positive and O negative. As humans, we are lucky. Cows have at least 800 different blood types. If that was us, blood banks would be a lot more difficult to stock.

Wound fluid is blood – only without the red blood cells, and therefore it is colourless. When an injury occurs, the area will soon redden, swell up and feel hot. This is because blood vessels surrounding the site of injury dilate, increasing blood flow to the injury. The capillary walls become more permeable, allowing fluid out. The fluid carries white blood cells, certain proteins and fats that are required for tissue repair. Red blood cells remain within the blood vessels as they are too large to squeeze through the gaps.

Here are four nutrients that can assist the blood with wound healing:


Iron helps to maintain the levels of haemoglobin in the blood, which is needed for the healing process. Iron is found in meat, seafood, beans, pulses, nuts, seeds, eggs, and green leafy vegetables.

Vitamin C

Vitamin C helps with the absorption of iron from food and also directly with the healing process.  It can help to eat an orange or a portion of berries with your iron tablets. Beetroot, broccoli and peppers are also rich in vitamin C.

Vitamin K

Vitamin K helps the proteins that coagulate the blood. Recent studies have found that applying creams that contain vitamin K to wounds reduced the time they took to heal. Dietary vitamin K is found in kale, spinach, cabbage, lettuce and other leafy greens.


In the initial healing phase, concentrations of zinc form around a wound, helping to start the healing process and also to protect the area from further damage. A deficiency in zinc is linked to slow wound healing. Foods that provide us with zinc include nuts, and seeds, seafood, eggs, lentils, meat and poultry.

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