Milk And Iron Absorption

Overview

Milk contains many components that are beneficial for various processes in the body. Iron is an essential element that can be obtained through the diet and enters the body as either heme or non-heme iron, depending on the food source. However, combining milk and iron-rich foods is not ideal for iron absorption.

Milk interferes with the absorption of iron from food or supplements. This is due to the calcium in the milk, which hinders heme and non-heme iron uptake.² It is advised to take any iron supplements at least 2 hours after consuming any calcium-rich foods or drinks to gain maximum benefits.

This article outlines the benefits and role that iron-rich foods and the components of milk play in the body and advises on the pairing of foods to maximise the absorption of all nutrients. 

Milk absorption

Components of milk

Cow milk is a substance that many of us may consume daily, be it in our morning coffee or on-the-go oatmeal. Milk is made up of water (87.5%), fats (3.9%), proteins, whey and casein (3.4%), lactose (milk carbohydrates) and minerals. There are also trace amounts of vitamins, enzymes and phospholipids present in milk.

Benefits of milk in the body

The following components of milk provide a lot of benefits to the body. 

• Protein: essential for muscle growth and development, cell repair and immune support 
• Calcium: allows bone development in younger children and keeps teeth healthy
• Potassium: an essential mineral that is involved in heart health. It helps with blood vessel dilation and the reduction of blood pressure
• Phosphorus: aids with bone development and growth in children. It is also involved in metabolic reactions and energy transfer in the body
• Vitamin D: helps to regulate the minerals calcium and phosphate in the body, which contribute to bone, teeth and muscle health 
• Vitamin B12: contributes to the health of the nervous system and supports immune function. It also helps with red blood cell formation
• Vitamin A: vital for the immune system, growth and development, and maintaining good vision

How is milk absorbed in the body?

Milk digestion begins in the stomach, where hydrochloric acid is present, creating an acidic environment for digestion. The protein in the milk is digested with the help of the enzyme proteases. The enzyme lipase aids in the digestion of fats, breaking them down into smaller fragments. At this stage, some byproducts can be absorbed into the stomach. 

In the small intestine, protein is broken down further into smaller fragments called amino acids and peptides, ready for absorption in the small intestine. Fats are also broken down further. Additionally, bile is released to help further hydrolyse fat into diglycerides, monoglycerides and free fatty acids.^1,3

The body also digests lactose in the small intestine with the help of an enzyme called lactase. Lactose begins as a sugar (disaccharide), which is broken down into two simple sugars (monosaccharides), glucose and galactose; the simple sugars are then absorbed into the bloodstream. People with lactose intolerance do not produce enough of the enzyme lactase and, therefore, cannot break down lactose present in milk or other dairy products. In this case, lactose stays in the gut and is fermented by bacteria, which causes symptoms such as bloating, stomach cramps, feeling sick and gas.

Now that the proteins, carbohydrates and fats have been broken down, the stage of further absorption continues. Diglycerides, monoglycerides and fatty acids (byproducts of fat) enter the lymph system and are released into the bloodstream, where they are used for energy, stored or contribute to growth and cell repair. Monosaccharides (products of lactose), peptides, amino acids (products of protein) and other minerals are absorbed into the bloodstream.³

Increase milk absorption

The pairing of various foods can increase the absorption of certain vitamins and minerals that are present in milk. Fat-soluble vitamins A and D that are contained in milk can be absorbed better when paired with foods high in fat, such as nuts, olive oil and avocado. Pairing foods such as an avocado sandwich or cereals high in nuts and seeds with your milk can be beneficial for the absorption of vitamins A and D present in cow’s milk. 

Vitamin D aids with the absorption of calcium in the body. Insufficient levels of Vitamin D lead to low levels of the hormone calcitriol, resulting in poor calcium absorption. This causes the body to use its calcium stores which consequently prevents the formation of strong bones. Some milk is fortified with vitamin D, helping the body absorb more calcium from the milk more efficiently.

Iron absorption

Benefits of iron In the body

Iron is a vital element and is used in DNA synthesis, oxygen and electron transport and various metabolic processes. The body also requires iron to make certain hormones. 

Iron is a component of haemoglobin which is a protein that is found in red blood cells. Haemoglobin transports oxygen to the body’s tissues and organs and carries carbon dioxide back to your lungs. Iron in muscle cells is called myoglobin and helps to store and release oxygen. Iron is also a component of various proteins in the body which play a part in respiration, metabolism, immune function and collagen production.⁴

A lack of iron in the body can lead to iron deficiency anaemia which can be confirmed by a blood test. If you are deficient in iron, you may experience the following symptoms:

• Fatigue 
• Pale skin 
• Headaches
• Heart palpitations 
• Cold hands and feet 

To prevent iron deficiency anaemia, it is advised to consume iron-rich foods.⁶ The recommended daily amounts for adults are outlined below.^8. 

• Men (over 18 years old ) – 8.7mg
• Women (19-50 years old)– 14.8mg
• Women (Over 50)– 8.7mg 

Our diet should provide us with sufficient levels of iron; however, in low socio-economic countries where iron-rich foods may be lacking, iron supplementation is advised. Ferrous sulfate can also be prescribed by your GP to prevent and treat iron deficiency anaemia. 

Sources of iron

You can obtain iron from the following iron-rich foods:

• Meat, particularly red meat and liver products  
• Iron-fortified products such as cereals and bread 
• Green leafy vegetables (spinach, broccoli, beet greens) 
• Dried fruits (apricots and raisins)

Forms of iron absorption

There are two types of iron that are absorbed in the small intestine via different pathways.

Heme iron (Fe2+) is found in animal food sources such as meat, fish and poultry and is more easily absorbed than non-heme iron. Non-heme iron (Fe3+) is found in plant foods and iron-fortified products and is less well absorbed.^5,

How is iron absorbed in the body?

Some dietary iron may need to be converted from its ferric form (Fe3+) to a ferrous ion (Fe2+) to be absorbed into the small intestine. Dietary iron absorption is controlled by the protein hepcidin, which derives from the liver.⁸

Fe3+ enters the intestine, where it comes in contact with a protein, and is reduced to the  Fe2+ form. Iron in the Fe2+ form is then transported into the intestinal epithelium to be absorbed into the bloodstream. It can remain in the Fe2+ form or can be bound to a protein. Iron uptake is regulated by the liver and a protein called hepcidin. If there is too much iron, it can be stored and excreted in the faeces. Once in the bloodstream, Iron is transported by a protein (transferrin) to the body’s cells for metabolic processes or to the bone marrow for the production of new blood cells. Heme iron is absorbed more readily and hence, iron deficiency is less common in a high-meat diet. 

Increasing iron absorption 

There are certain vitamins in foods that can increase the absorption of iron. There is evidence to show that vitamin C can increase iron absorption. Vitamin C in foods such as oranges, grapefruits, peppers as well as citric juices is a great enhancer of non-heme iron absorption. You can also purchase vitamin C in the form of ascorbic acid if your diet is lacking in vitamin C-rich foods. Some studies have also found that foods high in vitamin A and carotenoids (carrots, sweet potato, spinach, oranges) can enhance non-heme iron absorption.⁵

Certain foods may have an inhibitory effect on iron absorption. Cereals and legumes contain phytates (phytic acid) which are inhibitors of non-heme iron absorption. When soaked properly, phytate levels can be reduced; additionally, pairing beans or legumes with foods high in vitamin C or iron-rich (heme iron) sources such as meat can counteract the negative effect of phytate. There is evidence to show that polyphenols have a negative effect on iron absorption as they bind with non-heme iron in the intestine.⁶ Calcium-rich foods have also been linked with hindering the absorption of heme and non-heme iron, meaning that it’s best to consume any iron-rich foods or supplements at different times of the day than calcium supplements.^6,7

Summary

There are many benefits of milk in the body as it provides us with protein, fats, sugars and various vitamins and minerals. Vitamins in cow’s milk, such as vitamins A and D, are absorbed better when paired with foods high in fat. The way foods are paired can impact the absorption efficiency of various nutrients contained in those foods.

Iron also plays a vital role in the body especially when it comes to red blood cell formation. However, the efficiency of iron absorption can be blocked by foods high in phytates, calcium and polyphenols. It is best to keep iron-rich foods separate from products such as cow’s milk as calcium in the milk can hinder iron absorption.