11 Questions You Are Wondering About Vitamin D

3. What Foods Provide Vitamin D?

Very few foods naturally contain vitamin D. Fortified foods provide most of the vitamin D in diets. Check the Nutrition Facts label for the amount of vitamin D in a food or drink.

• Milks can be fortified with vitamin D, with approximately 3 mcg (120 IU) per glass. Many plant-based alternatives, such as soy milk, almond milk, and oat milk, can be similarly fortified. However, foods made from dairy, such as cheese and ice cream, are generally not fortified.
• Vitamin D is added to many breakfast cereals and some brands of orange juice, yogurt, margarine and other food products.
• Fatty fish (such as trout, salmon, tuna, and mackerel) and cod liver oils are among the best natural sources of vitamin D.
• Beef liver, egg yolk and cheese contain small amounts of vitamin D.
• Mushrooms contain some vitamin D. Some mushrooms have been exposed to ultraviolet light to increase their vitamin D content.

4. Can I Get Vitamin D from the Sun?

Your body produces vitamin D when your bare skin is exposed to the sun. Most people get at least some vitamin D this way. But clouds, smoke, fog, old age and dark skin reduce the amount of vitamin D your skin produces. Additionally, your skin does not make vitamin D from sunlight coming through the window.

Ultraviolet radiation from sunlight can cause skin cancer, so it's important to limit the time you spend in the sun. Although sunscreen limits vitamin D production, health experts recommend using sunscreen with a sun protection factor (SPF) of 15 or more whenever you stay in the sun for more than a few minutes.

5. What Types of Vitamin D Dietary Supplements Are Available?

Vitamin D is found in multivitamin / multimineral supplements. It is also available in dietary supplements that contain vitamin D alone or vitamin D along with several other nutrients. The two forms of vitamin D in supplements are D2 (ergocalciferol) and D3 (cholecalciferol). Both forms increase vitamin D in your blood, but D3 can raise it higher and for longer periods of time than D2. Because vitamin D is fat-soluble, it is best absorbed when taken with a meal or snack that contains some fat.

6. Am I Getting Enough Vitamin D?

Because you get vitamin D from food, sunlight, and dietary supplements, one way to tell if you're getting enough is a blood test that measures the amount of vitamin D in your blood. In the blood, a form of vitamin D known as 25-hydroxyvitamin D is measured in nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). One nmol/L is the same as 0.4 ng/mL.

• Levels of 50 nmol/L (20 ng/mL) or above are sufficient for bone and general health for most people.
• Levels below 30 nmol/L (12 ng/mL) are very low and can weaken your bones and affect your health.
• Levels above 125 nmol/L (50 ng/mL) are very high and can cause health problems.

Some people are more likely than others to have problems getting enough vitamin D:

• Breastfed babies. Breast milk alone does not provide sufficient amounts of vitamin D to babies. Breastfed babies should be given 10 mcg (400 IU) of vitamin D supplements every day.
• Older adults. As you age, your skin's ability to produce vitamin D when exposed to sunlight decreases.
• People who rarely expose their skin to sunlight because they don't go outside or keep their bodies and heads covered. Sunscreen also limits the amount of vitamin D your skin produces.
• Dark-skinned people. The darker your skin, the less vitamin D you get from sunlight.
• People with conditions that limit fat absorption, such as Crohn's disease, celiac disease, or ulcerative colitis. This is because the vitamin D you consume is absorbed in the intestine along with fat, so if your body has trouble absorbing fat, it will also have trouble absorbing vitamin D.
• People who are obese or have had gastric bypass surgery. They may need more vitamin D than other people.

7. What Happens If I Don't Get Enough Vitamin D?

Vitamin D deficiency in children causes rickets, a disease in which bones become soft, weak, deformed and painful. Vitamin D deficiency in teenagers and adults causes osteomalacia, a disease that causes bone pain and muscle weakness.

8. What Are Some Effects of Vitamin D on Health?

Scientists are studying vitamin D to better understand how it affects health. Here are a few examples of the results of this research:

Bone health and osteoporosis: Long-term vitamin D and calcium deficiencies cause your bones to become brittle and break more easily. This condition is called osteoporosis. Millions of older women and men have osteoporosis or are at risk of developing the condition. Muscles are also important for healthy bones because they help maintain balance and prevent falls. A deficiency of vitamin D can cause weak, sore muscles.

Getting the recommended amounts of vitamin D and calcium from foods (and supplements if necessary) will help maintain healthy bones and prevent osteoporosis. Taking vitamin D and calcium supplements slightly increases bone strength in older adults, but it is not clear whether they reduce the risk of falls or broken bones.

Cancer: Vitamin D does not seem to reduce the risk of breast, colon, rectum, or lung cancer. It is not clear whether vitamin D affects the risk of prostate cancer or the chances of surviving this cancer. Very high vitamin D levels may even increase the risk of pancreatic cancer.

Clinical studies show that although vitamin D supplements (with or without calcium) do not affect the risk of cancer, they may slightly reduce the risk of dying from this disease. More research is needed to better understand the role vitamin D plays in cancer prevention and cancer-related death.

Heart disease: Vitamin D is important for a healthy heart and blood vessels and normal blood pressure. Some research shows that vitamin D supplements may help lower blood cholesterol levels and high blood pressure, two of the main risk factors for heart disease. Other studies show no benefit. If you are overweight or obese, taking vitamin D and calcium in doses above 20 mcg (800 IU) per day may actually raise your blood pressure. Overall, clinical studies have found that vitamin D supplements do not reduce the risk of developing heart disease or dying from it, even if you have low blood levels.

Depression:  Vitamin D is necessary for your brain to function properly. Some studies have found a link between low blood vitamin D levels and an increased risk of depression. However, clinical studies have shown that taking vitamin D supplements does not prevent or relieve symptoms of depression.

Multiple sclerosis: People living near the equator have more sun exposure and higher levels of vitamin D. They also rarely develop multiple sclerosis (MS), a disease that affects the nerves that carry messages from the brain to the rest of the body. Many studies find a link between low blood vitamin D levels and the risk of developing MS. However, scientists have not actually studied whether vitamin D supplements prevent MS. Clinical studies in MS patients show that taking vitamin D supplements does not prevent symptoms from worsening or recurring.

Type 2 diabetes: Vitamin D helps your body regulate blood sugar levels. However, clinical trials in people with and without diabetes show that vitamin D supplementation does not improve blood sugar levels, insulin resistance, or hemoglobin A1c levels (the average blood sugar level over the past 3 months). Other research shows that vitamin D supplements do not prevent most people with prediabetes from developing diabetes.

Weight loss: Taking vitamin D supplements or eating foods rich in vitamin D will not help you lose weight.

9. Can Vitamin D Be Harmful?

Yes, taking too much vitamin D can be harmful. Very high levels of vitamin D in your blood (higher than 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. Excessively high vitamin D levels can cause kidney failure, irregular heartbeats, and even death. High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements. You can't get much vitamin D from sunlight because your skin limits the amount of vitamin D it produces.

Daily upper limits for vitamin D include intakes from all sources (food, beverage, and supplements) and are listed below in micrograms (mcg) and international units (IU):