Why you need vitamin D
Vitamin D is also important for a healthy immune system. It regulates your immune system activity and studies show it might help boost your natural defenses.
It’s also important for protecting your body from autoimmunity, which happens when your immune system attacks your own tissues and cells.
You get vitamin D mostly from the sun. Sun rays energize cholesterol in your skin, and the cells convert it into a molecule called pre-vitamin D. This goes to your liver and is converted into cholecalciferol and then to your kidneys, where it is converted to the active form of vitamin D called calcitriol.
You can also get vitamin D from fortified foods. Only a few natural foods contain vitamin D, so it is commonly added to some foods like cereals, milk, and orange juice. When you consume vitamin D, you get an inactive form, which your liver and kidneys convert to the active form.
The recommended daily allowance for adults age 19 years and older is 600 international units (IU) daily. If you’re over 70 years of age, you should get 800 IU of vitamin D every day.
Why you don’t get enough vitamin D
Vitamin D deficiency is most commonly caused by a lack of sun exposure. The sun is the most natural way to get vitamin D, but it’s hard to get enough because you also need to protect your skin from sun damage. Some groups of people tend not to get enough vitamin D. Those most prone to deficiencies include people who:
- Live in cold climates and spend a lot of time inside
- Work inside
- Live in long-term care facilities
- Wear sunscreen
- Wear long, protective clothing
Older people and people with darker skin tones are also likely to get less vitamin D from the sun. Older people have less cholesterol in the skin and people with darker skin tones have more melanin, which slows down UV ray absorption. Both of these stop the sun from making vitamin D in older or darker skin tones.
Some health conditions can cause problems absorbing vitamin D and can lead to low vitamin D levels. These conditions include:
Low vitamin D symptoms
Insufficient vitamin D can cause different symptoms — including:
- Muscle aches
- Muscle weakness
- Muscle spasms — called tetany
- Bone pain
- Rickets in children
- Irregular bone growth in children
- Weakened bones
- Softened bones — called osteomalacia
- Loss of calcium
- Getting sick a lot
People with autoimmune diseases are likely to have low vitamin D, but how this happens is still unclear.
The symptoms of low vitamin D can look like other health problems, so it’s important to talk to your doctor. They can do blood tests to check your levels. If you have severely low levels, you might need to take a higher amount to correct the deficiency.
Are you getting enough vitamin D?
Some doctors recommend that you expose your skin to the sun for 5 to 15 minutes three times a week to prevent vitamin D deficiency. Some people might need more time to get enough vitamin D, but this isn’t recommended. Too much time in the sun without protection can cause skin cancer.
So the best way to know if you’re getting enough vitamin D is if you get the recommended amount in your diet. These recommendations will help you reach the proper level:
- Drink cow’s milk
- Drink fortified non-dairy milk
- Eat fortified foods
- Take a vitamin D supplement
To make sure you’re getting enough from food, you’ll need to track your intake, calculate, and add in other sources. For example, one serving of fortified cereal usually has only about 40 to 50 IUs of vitamin D. This means you’ll have to eat or drink a few other foods — or take a supplement — to make sure you’re getting enough.
Vitamin D is also fat-soluble. To properly absorb vitamin D supplements, have some healthy fat with your meal.
If you need help with your diet, talk to a doctor or a nutritionist. They can also help you find the right vitamin D supplement for you.
Harvard T.H. Chan School of Public Health: "Vitamin D."
Journal of the Academy of Nutrition and Dietetics: "Dietary fat increases vitamin D-3 absorption."
Merck Manual Consumer Version: "Vitamin D Deficiency."
Oregon State University Linus Pauling Institute: "Vitamin D."
St. Luke’s Health: "4 Signs You Have a Vitamin D Deficiency."
University of Rochester Medical Center: "Vitamin D."
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