Vitamin D

Sunlight helps your body stay strong.

When sunlight hits your skin, it makes a special thing. This helps your body take in minerals. These minerals keep your bones healthy.

You can also get this from food. Some milk and cereal have it added. In the past, people used oil from fish. This helped children stay well. It is a very important part of being healthy!

Vitamin D helps your body use calcium. Calcium is a mineral that keeps bones strong.

There are two main types. One is vitamin D2. The other is vitamin D3.

Your body can make its own vitamin D. This happens when sunlight hits your skin. The sun's light helps the skin make vitamin D3.

You can also get it from food. Many people drink milk with vitamin D added. Some breakfast cereals have it too.

Once you have it, your body must change it. First, your liver changes it into calcifediol. Then, your kidneys change it again. This makes calcitriol. Calcitriol is the active form. It works by attaching to vitamin D receptors. These receptors are parts inside your cells.

In the past, people used cod liver oil. This oil comes from fish. It helped stop a disease called rickets. Rickets can make bones soft or curved. Scientists found vitamin D in 1922. Adolf Windaus won a Nobel Prize for his work.

Vitamin D is a special group of compounds that helps your body work correctly. Its most important job is helping your intestines absorb calcium and phosphate. These two minerals are very necessary for keeping your bones strong and healthy.

There are two main types of this vitamin. One is called vitamin D2, or ergocalciferol. The other is vitamin D3, or cholecalciferol. Most people get more of their vitamin D from their skin than from food.

Your body has a very clever way of making its own vitamin D. When sunlight hits your skin, it provides ultraviolet B radiation, also known as UVB. This light hits the deeper layers of your skin's epidermis. This process creates cholecalciferol inside your body.

Once it is made, your body must change it through a few steps. First, your liver turns it into a substance called calcifediol. Next, your kidneys and some immune cells turn it into calcitriol. Calcitriol is the active form that finally attaches to vitamin D receptors in your cells.

Scientists worked for a long time to understand this vitamin. In the 1800s, people used cod liver oil to treat various health issues. People in Europe noticed that children who ate this oil did not get rickets. Rickets is a condition that can make bones soft or curved. In 1922, researchers finally identified and named vitamin D. A scientist named Adolf Windaus did important work on these structures. He even won the Nobel Prize in Chemistry in 1928 for his discoveries.

There are many specific facts about how we find vitamin D today. In the United States, many people get it from fortified foods. This means companies add vitamin D3 to milk and many breakfast cereals.

Doctors often measure a person's vitamin D levels by looking at a substance called 25(OH)D in their blood. This helps them see if a person has enough to stay healthy. Some experts say a level above 50 nmol/L is needed to be fully sufficient.

Understanding vitamin D helps us see how our environment affects our health. Many people live in cities where they might not see enough direct sunlight. People also use sunscreen to protect their skin from the sun. Both of these things can mean a person might need more vitamin D from food.

This is why many governments have programs to add the vitamin to common foods. It is a way to make sure everyone gets what they need to grow strong. Just like a battery needs a charge, our bodies need these tools to function.

Vitamin D is a group of structurally related, fat-soluble compounds. These compounds are essential for many biological functions. Their most critical role is increasing the intestinal absorption of calcium and phosphate. These minerals are necessary for building and maintaining strong bones.

Unlike the other twelve essential vitamins, vitamin D is only conditionally essential. This means the body can produce it through sunlight exposure. Without enough vitamin D, humans can develop serious bone conditions. These include rickets in children and osteomalacia in adults.

The body uses a specific biological pathway to create and activate this vitamin. Most vitamin D comes from the skin rather than from food. When the skin is exposed to ultraviolet B (UVB) radiation, it triggers a process. This radiation hits the deeper layers of the epidermis. This causes the synthesis of cholecalciferol, also known as vitamin D3. This is the first step in a complex chain of chemical changes.

Once cholecalciferol is produced, it must undergo two stages of hydroxylation. First, the liver converts cholecalciferol into calcifediol. This substance is also known as 25-hydroxycholecalciferol. Doctors measure the levels of these metabolites in the blood to check vitamin D status. This measurement is called 25(OH)D. Next, the kidneys and certain immune cells perform a second hydroxylation. This step turns calcifediol into calcitriol. Calcitriol is the biologically active form of the vitamin.

The active form, calcitriol, works by interacting with specific parts of our cells. It attaches to vitamin D receptors, which are nuclear receptors found in many tissues. These receptors act as transcription factors. This means they help control how genes are expressed in the body. Specifically, they modulate proteins that help the intestine absorb calcium. This process is vital for maintaining the correct levels of calcium and phosphorus in the blood. The vitamin D receptor is part of a larger family of steroid hormone receptors. These receptors are found in various organs, including the bone, kidney, and parathyroid gland.

The history of vitamin D is a story of scientific discovery and observation. For a long time, people in northern Europe used cod liver oil for medicinal purposes. By the 1820s, researchers noticed that children fed this oil did not develop rickets. In 1922, researchers finally identified and named the specific vitamin. Elmer McCollum was a key figure in this discovery. He proved that the factor in cod liver oil was different from vitamin A. He named it vitamin D because it was the fourth vitamin identified. Adolf Windaus later won the Nobel Prize in Chemistry in 1928 for his work on sterols. His research helped clarify the chemical structure of these compounds.

Today, vitamin D levels are a major focus of public health. Many people face deficiency due to modern lifestyles. Urban living often means less direct sunlight exposure. People also use sunscreen to protect against skin cancer. Because of this, many countries use food fortification programs. In the United States, vitamin D3 is added to cow's milk and plant-based milk substitutes. It is also added to many breakfast cereals. This helps ensure that people receive enough vitamin D orally.

Understanding vitamin D deficiency requires looking at specific measurements. Scientists use serum 25(OH)D concentrations to define health levels. Different organizations suggest different targets. The US Institute of Medicine notes that levels below 30 nmol/L increase rickets risk. At this low level, calcium absorption can drop from 80% to as low as 15%. To prevent osteomalacia in the elderly, levels should be above 40 nmol/L. For full health needs, some experts suggest a level above 50 nmol/L. These numbers show how important precise amounts are for our bodies. Vitamin D connects our environment, our diet, and our internal biology to keep us healthy.