Vitamin D is a fat-soluble vitamin that has many important functions in the body. It is a unique nutrient because we get it from food sources, but it is also something our body makes. In fact, we can get vitamin D in three ways-from sunlight, food, and vitamin D supplements.
Exposure to ultraviolet light triggers the conversion of cholesterol in our skin into vitamin D3, which is a type of vitamin D. D3 then enters the bloodstream and is transported to the liver and kidneys, where it is converted to its biologically active form (calcitriol). Because our body naturally produces vitamin D through sunlight exposure to the skin, it is often referred to as the sunlight vitamin.
What is the role of vitamin D in the body?
Most of us believe that vitamin D is important for bone growth, and of course, it is. Vitamin D helps the absorption of calcium and helps to form and maintain strong bones. When you don’t get enough vitamin D, you are at risk for diseases such as rickets in children and osteomalacia in adults. This is why the US government started adding vitamin D to milk in the 1930s-rickets was a major health problem at the time.
But vitamin D is not only essential for healthy bones-it actually has several other important functions in the body, including maintaining the health of the muscles, nerves, and immune system and regulating proper cell growth. In addition, it can also reduce the risk of certain types of autoimmune diseases (such as multiple sclerosis) and provide protection against diabetes, cardiovascular disease, dementia, and certain types of cancer. However, most of the evidence comes from observational studies, so more intervention studies on vitamin D supplements are needed to determine the role of vitamin D in these diseases.
How much vitamin D do you need?
Life stage
Recommended amount
From birth to 12 months
10 micrograms (400 international units)
Children 1-13 years old
15 micrograms (600 international units)
Adolescents 14-18 years old
15 micrograms (600 international units)
Adults 19-70 years old
15 micrograms (600 international units)
Adults 71 years and older
20 micrograms (800 international units)
Pregnant and breastfeeding women
15 micrograms (600 international units)
At present, there is a lot of scientific debate about the optimal intake of vitamin D. The official recommended dietary intake (RDA) set by the Institute of Medicine (IOM) is 600 International Units (IU) per day for adults aged 19-70 and 800 IU per day for adults over 70. RDA provides the daily amount needed to maintain healthy bones and normal calcium metabolism and is based on minimal sunlight exposure. But according to the latest research, many groups recommend taking more vitamin D. For example, the Endocrine Society recommends a daily intake of 1,500 IU to 2,000 IU to achieve adequate serum vitamin D levels.
What are the symptoms and signs of vitamin D deficiency?
What is the best way to get enough vitamin D? One way is through exposure to sunlight. Only 10-15 minutes of sunlight can provide 3,000-20,000 IU. The problem is that the amount of vitamin D we get from sun exposure varies greatly depending on factors such as geographic latitude and skin color. The sunlight in northern latitudes is usually weak, resulting in less vitamin D synthesis. In addition, people with darker skin usually need more sunlight to synthesize vitamin D, because melanin reduces the skin’s ability to produce vitamin D from sunlight.
Vitamin D deficiency has re-emerged as a global health problem. About 1 billion people in the world lack vitamin D. Some experts believe that low vitamin intake, coupled with restrictions on UV exposure (such as staying indoors, using sunscreen, and using protective clothing to completely cover the skin) leads to a general deficiency of vitamin D status. The elderly and individuals who are hospitalized or in nursing homes are, particularly at risk. Many of them not only do not have adequate sunlight, but their dietary intake may also be limited, and/or kidney function may be impaired, which limits the conversion of vitamin D to its active form.
Many people with vitamin D deficiency have no symptoms. Other people may experience signs or symptoms, such as muscle pain or cramps, bone pain, weakness, fatigue, and mood changes. With chronic vitamin D deficiency, infants and children may develop rickets, which are characterized by soft bones and bone deformities, such as bent legs. In adults, chronic vitamin D deficiency can lead to osteomalacia, which is characterized by weak and soft bones and may cause frequent fractures.
6 foods with vitamin D
In the absence of UV exposure, adequate vitamin D intake is essential to prevent deficiency. However, there are relatively few natural food sources of vitamin D. Most of the vitamin D in the American diet comes from fortified foods. The following are the best food sources of vitamin D:
- Fatty fish such as salmon, trout and mackerel
A 3 ounce serving of rainbow trout provides 645