Vitamin C improves the absorption of iron. Vitamin C is also needed to make collagen.
It's really important to get all our needed vitamins and minerals.  We get energy from food. A lot of that energy comes from electron transfer.  How does that work? Well electron transfer generates heat.
Electricity is a form of fire. This is why we call a firewall a firewall.
We can use the heat generated by electron transfer to raise the temperature of a chemical reaction, and thereby increase the rate of the reaction and the yield of the reaction. (Consider the relationship between the temperature of a chemical reaction and the rate and yield of the reaction.)
We also use the chemicals in food as building blocks for protein, DNA, fats, and other molecules needed to make cells. We need a lot of protein to make new cells. Just think: we need protein to make DNA, and we have to replicate our DNA in order to create new cells. 
So getting enough vitamin C is one way of improving the absorption of iron. It also helps our immune system. We oxidize vitamin C to get energy. Oxygen is an electron acceptor. Oxygen accepts electrons from vitamin C.  We use the heat generated by electron transfer to break down molecules and substances. Our immune system specializes in breaking down substances that need to be removed.
The energy we get from vitamin C helps us break down substances that the immune system wants to remove. These substances are broken down in a chemical reaction, and the energy from vitamin C increases the rate of the reaction. The energy from vitamin C can also start a reaction that requires a high initial temperature.
Another way of improving the absorption of iron is having a healthy and ethical diet.  A healthy and ethical diet improves the absorption of vitamins and minerals and other nutrients. A healthy and ethical lifestyle improves the absorption of vitamins and minerals and other nutrients.
I am a vegan and I try my best to have an ethical diet. An ethical diet consists of foods and drinks that are produced without hurting any plants, animals, or other forms of life.
I hope this helps. To summarize, two ways of improving iron absorption are getting enough vitamin C and having a healthy and ethical diet and lifestyle. A third way of improving iron absorption is to prevent stress, remove stress, or cure feelings of stress. Stress actually affects the concentration of hormones in the bloodstream, by adding stress hormones to the bloodstream. Our digestion is connected to the hormones in the bloodstream, and the concentration of those hormones. The healthier our hormones, the easier it is to digest. 
 Vitamins A, B12, C, D, E, and K are some examples of vitamins. Iron, calcium and potassium are some examples of minerals.
 We actually have many ways of getting energy from food. One way is by oxidizing an electron donor, like glucose or vitamin C. Oxygen is an electron acceptor. Oxygen can accept electrons from glucose and vitamin C, and this electron transfer generates a lot of energy in the form of heat. Another way of getting energy from food is by breaking molecular bonds. In the process called glycolysis, we oxidize glucose, and we also break chemical bonds in glucose. The glucose molecule is capable of holding more energy when it is fully intact. After one of its molecular bonds is broken, the glucose molecule is capable of holding less energy. The energy that gets released is released in the form of heat. So that is a second way of getting energy from the molecules in food. There is a third way of getting energy from the molecules in food. When we eat or drink electrolytes, we are able to create ions from the electrolytes. Electrolytes are sources of ions. Calcium carbonate is a source of calcium ions. We can get Ca2+ ions from calcium carbonate. We can get calcium ions and potassium ions from foods containing calcium and potassium. We can get K+ ions from food containing potassium. These ions are capable of creating a voltage difference. These ions have electric potential energy. So we can get electric potential energy from ions. We can get energy from ions in the form of electric potential. When you put Ca2+ ions or K+ ions in the axon of a neuron, it creates a voltage difference with the outside of the cell membrane. This voltage difference is sometimes called a membrane potential. We need Ca2+ ions and K+ ions in order to release action potentials in our neurons. We need calcium and potassium in order to release action potentials in our brains and in our muscles and in our nervous tissues. So calcium and potassium are important for brain function and muscle function. To summarize this footnote, we have discussed three ways of getting energy from food. One way is by oxidizing an electron donor, like glucose or vitamin C. One way is by breaking molecular bonds. We break molecular bonds in glucose during the process of glycolysis. We also oxidize glucose during the process of glycolysis. A third way of getting energy from food is by creating ions out of electrolytes. When you put an electrolyte in water it dissolves and forms ions. That's one reason we need water. Water is a solvent. It is super important to be hydrated and drink enough water. Two forms of hydration are drinking water and showering. I want to add that electrolytes are super important. A lot of people have a calcium deficiency or a potassium deficiency. The US government creates fortified drinks that have calcium and other essential vitamins and minerals. The US government sells these fortified drinks in grocery stores. It is important to know what foods and drinks are safe for your unique and individual biology. It is important to have safe food, safe drink, and safe air. A food that is safe for one person might not be safe for another person, and one example is a food that generates an allergic reaction in a population of people. So we can really figure out what foods and drinks are safe for us, and get dietary sources of all the vitamins and minerals we need. We can figure out what foods and drinks are safe for us, and get dietary sources of electrolytes. We can figure out what foods and drinks are safe for us, and get dietary sources of proteins, carbohydrates, fats, vitamins, minerals, electrolytes, fiber, and water. Fiber helps us digest. Fiber is super important. I hope this helps.
 We need protein in order to get the nucleic acids that are needed to make new DNA. We also need protein in order to get the amino acids that are needed to make new proteins in the ribosome. We need to get enough protein in our diet to make new cells and proteins.
 Oxygen is an electron acceptor and vitamin C is an electron donor. Glucose is also an electron donor. We oxidize vitamin C to get energy from vitamin C. When we oxidize vitamin C, oxygen accepts electrons from vitamin C. We oxidize glucose to get energy from glucose. When we oxidize glucose, oxygen accepts electrons from glucose. We oxidize glucose in a process called glycolysis, which is part of cellular respiration. The electron transfer that occurs during the process of oxidation generates heat, and we use that heat to power chemical reactions and to make ourselves warm.
 Eating too much makes it harder to digest, and eating too little makes it harder to digest. An unhealthy diet makes it harder to digest. So it makes sense that a healthy and ethical diet makes it easier to digest food and absorb iron. It's important to get enough iron and to find ethical foods that are rich in iron. The website nutrition.gov gives dietary sources for iron and other minerals. The website nutrition.gov gives dietary sources for all of the vitamins, minerals, and nutrients that we need.
 Diet and stress are two risk factors for disease, and this is an adage in medicine. A risk factor is a factor that increases or decreases a risk. An unhealthy diet increases the risk of disease. Stress increases the risk of disease. A healthy diet decreases the risk of disease. When we cure feelings of stress we decrease the risk of disease. And the reason for this is: when we cure stress we improve the health of our blood. This topic, blood health, is important. We don't want to have too much stress in our blood and we don't want to have too much sugar in our blood. Everyone can have perfect blood health if they have a correct diet, receive competent medical care, and take all of the medicines that they need to take. Medicine is extremely important, and the field of medicine is a fascinating field. The US government is so advanced that the US government has already cured every disease, by means of medicine. For every disease there is a cure. We can use medicine to cure any disease. Medicine is one of the best creations in the history of planet Earth and in the history of the universe. In order to cure many diseases, illnesses, and health problems, we need to take medicine every day, and that routine of taking medicine every day is the cure. A lot of people say, "It's only a disease if it's left untreated." And we treat it with medicine, taking medicine as often as we need to take medicine.