Vitamin D - Are You Getting Enough?

Vitamin D, the sunshine vitamin, is most notably known for regulating calcium and maintaining healthy bones. However, vitamin D is also similar to a hormone, in that it regulates many different process throughout the entire body. It’s likely that if you’re not supplementing, you’re vitamin D deficient or suffering from vitamin D insufficiency and impairing your health.


How Do We Synthesize Vitamin D From the Sun?

Our bodies have the ability to use sunlight to help synthesize vitamin D. Vitamin D production in the skin is triggered by sunlight, specifically ultraviolet-B (UVB) rays. Sunlight exposure converts 7-dehydrocholesterol (7-DHC) in the skin to previtamin D3, then to vitamin D3. This synthesized D3, or D2 and D3 consumed from the diet, are converted by the enzyme 25-hydroxylase to 25-hydroxyvitamin D [25(OH)D] in the liver. 25(OH)D, or calcidiol, is then converted in the kidneys by 1-hydroxylase to the active form of vitamin D; 1,25-dihydroxyvitamin D [1,25(OH)2D]; calcitriol. (1

Unfortunately, a very large portion of the world does not get enough vitamin D from the sun. One of the reasons being, is that for a lot of us, it’s actually impossible for us to make vitamin D from the sun for months out of the year.

The zenith angle is the angle of the sunlight that reaches the Earth, which also determines how much of the ozone layer the sun must pass through. This angle depends on the time of day, time of the year, and latitude. When the sun is lower, its rays must pass through more ozone, and causes more UVB radiation to be absorbed. This is why the morning and evening isn’t the best time to synthesize vitamin D from the sun, because the sun is too low in the sky.

A good rule of thumb is that if your shadow is longer than you are tall, then it is likely that you will not be able to make vitamin D from the sun, because your skin won't receive enough UVB rays.

During the colder months of the year the sun is low in sky all day long, which means little to no UVB rays will make it down to the earth, depending on where you live. The farther you are away from the equator, the less likely you’ll be able to make vitamin D all year long. (1)

Those living more north, i.e. Boston (42°N) or Edmonton, Canada (52°N), can’t make enough vitamin D from the sun for 4-5 months out of the year and are at a greater risk of vitamin D insufficiency or deficiency. (2)

Pollution can also reduce the amount of UVB rays that pass through the atmosphere. You can still make vitamin D on a cloudy day, but you will likely need more sun exposure on those days. (3) It’s good to understand that you can’t get vitamin D through windows, because UVB does not penetrate glass.

It’s common to use sunscreen to protect us from developing skin cancer. However, sunscreen with SPF 15 will absorb 99% of UVB rays, which decreases vitamin D synthesis in the skin by 99%. (1)  

While sunscreen definitely blocks UVB rays and thus vitamin D synthesize, people don’t apply sunscreen often enough or cover every inch on their bodies with it, so it’s likely that people still synthesize some vitamin D when they apply sunscreen.

Because darker skin persons have more melanin, which is very efficient at absorbing UVB rays like sunscreen, they need more exposure to sunlight and/or need to consume adequate amounts of vitamin D through diet. (1)

For most people living in a location where the sun is high enough in the sky, 5-30 minutes between 10 am and 3 pm twice a week on the face, arms, legs, or back without sunscreen should be sufficient time to synthesize adequate vitamin D. Tanning beds that emit 2-6% UVB also work. (3) However, UV radiation can cause skin cancer. So ideally, you don’t want to use tanning beds, and you don’t exactly want to bake in the sun all day long either. 

If you’re older, you’ll need more sun exposure. 70 year olds have 75% less 7-dehydrocholesterol, which is the precursor to vitamin D3. The equates to having a 75% reduced ability to make vitamin D from the sun. (1)


How Much Vitamin D Do We Need to Consume?

For the average person, how much you should consuming on a daily basis is listed below according to age.

Recommended Dietary Allowances (3)


Vitamin D

0-12 months

400 IU

1-70 years old

600 IU (includes pregnancy and lactation)

>70 years old

800 IU

The American Academy of Pediatrics (AAP) recommends that breastfed infants should receive 400 IU/day of vitamin D. When they are weaned from breastmilk to more than 1,000 ml/day of vitamin D fortified formula, they can stop receiving the supplemental vitamin D. Non-breastfed infants who are consuming less than 1,000 ml/day of formula also need to be supplemented with 400 IU/day of vitamin D. (3)

In order to see where your vitamin D levels are at, serum 25(OH)D is the best way to check vitamin D status. 25(OH)D has a half life of 15 days, and indicates how much you are synthesizing from the sun, as well as getting though diet. (3)

As of right now, it appears that optimal serum 25(OH)D has not been established. However, there is a range for good health. You definitely need at least 50 nmol/L (20 ng/mL) to prevent deficiency, but you don’t want to be at 125 nmol/L (50 ng/mL) since there is evidence that this higher level can negatively affect health. (3)

More than 30 ng/mL 25(OH)D is needed in order to maximize the health benefits of vitamin D. During the colder months when vitamin D cannot be synthesized in our skin via the sun, 800-1,000 IU of D3 take each day is likely needed to maintain 30 ng/mL. (1)  Upwards of 1500 – 2000 IU may be needed to raise vitamin D levels above 30 ng/ml. (4) Since greater than 32 ng/mL is needed to maximize intestinal calcium absorption, that might be a good target. (1)

Vitamin D toxicity is rare, and doesn’t occur unless 25(OH)D levels are above 150 ng/mL. (1) The sun does not cause vitamin D toxicity, only ingested vitamin D. (3) Chance of toxicity is low with intakes less than 10,000 IU per day. Below is the upper limit to what amounts are considered safe. The table below tells you the maximum amount of vitamin D you should consume daily.

Tolerable Upper Intake Levels (ULs) for Vitamin D (3)


Vitamin D

0-6 months

1,000 IU (25 mcg)

7-12 months

1,500 IU (38 mcg)

1-3 years

2,500 IU (63 mcg)

4-8 years

3,000 IU (75 mcg)

9 years and older

4,000 IU (100 mcg)


Vitamin D Deficiency and Insufficiency

Vitamin D deficiency is a pandemic. Vitamin D deficiency is most notably known for reducing bone health, including rickets in children, osteoporosis, osteopenia, osteomalacia, and increased risk of bone fractures in adults. (1)

Serum 25(OH)D less than 20 ng/mL indicates vitamin D deficiency, and levels between 21-29 ng/mL indicate insufficiency. (1)

About 50% of the world has vitamin D insufficiency, and 1 billion people are vitamin D deficient. Not having adequate levels of vitamin D have been linked to diseases and illnesses. Vitamin D deficiency itself is an independent risk factor for total mortality. (5)

Low 25(OH)D is associated with higher parathyroid hormone (PTH), because PTH helps to maintain serum calcium levels by breaking down and removing calcium from the bone. (1)

Poor vitamin D status substantially increases the risk for dementia and Alzheimer disease, and is related to vascular dysfunction, stroke, and brain atrophy. Once cognitive decline occurs, vitamin D status is at a greater risk, because dietary changes and reduced outdoor activity are likely. (6)

There are a few different reasons that put people at risk of vitamin D deficiency. Living at higher latitudes in the United States is associated with risk of cancer, including colon, prostate, breast, and others. At higher latitudes, the sun is lower in the sky more often, which means its less likely that persons living at higher latitudes will be able to synthesize adequate vitamin D from the sun.  Living at higher latitudes is also associated with type 1 diabetes, multiple sclerosis, schizophrenia, depression, and hypertension.

Vitamin D is a fat soluble vitamin, so its absorption in the intestinal tract depends on the body’s ability to absorb fat. Fat malabsorption is associated with liver disease, cystic fibrosis, celiac disease, Crohn’s disease, and ulcerative colitis if the terminal ileum is inflamed. People with digestive disorders may also have lower intakes of vitamin D containing foods. (3) Those who have a difficult time digesting, absorbing, and metabolizing fats may be at risk for vitamin D deficiency.

Obesity is associated with vitamin D deficiency, because fat cells take up the vitamin D and keep it from being usable. A body mass index (BMI) ≥30 is associated with lower levels of serum 25(OH)D. Higher levels of subcutaneous fat stores and holds on to vitamin D, preventing its release into the circulation. (3)

Some medications affect vitamin D status. Corticosteroids reduce calcium absorption and impair vitamin D metabolism, which is why they are associated with decreased bone health. Cholesterol lowering drugs like cholestyramine, which decreases fat and fat soluble vitamin absorption, can also decrease vitamin D absorption. An epilepsy medication called phenytoin, which is used to control seizures, causes the liver to metabolism vitamin D to inactive compounds. (3)

 Kidney issues can also put someone at risks of vitamin D deficiency. The kidneys play a large role in converting vitamin D to its active form.  When the cells of the kidneys are damaged, it may disable the kidneys ability to convert 25(OH)D to active vitamin D. (3)

Older adults are at an increased risk of vitamin D deficiency because they cannot synthesize vitamin D from the sun as well, they are also less likely to spend time outdoors and to eat less foods containing vitamin D. (3)


Vitamin D Regulates Calcium, Phosphorus, and Bone Health

Vitamin D is primarily known for increasing intestinal calcium absorption and maintaining calcium and phosphate levels to ensure healthy bone mineralization. Inadequate vitamin D leads to soft or brittle bones, and having adequate vitamin D prevents rickets in children, and osteomalacia in adults. (3)

Low vitamin D is associated with osteoporosis. Osteoporosis causes bone deterioration, which leads to increased risk of fractures. Vitamin D and calcium work together to support bone health, so it’s important to ensure adequate intakes of both. (3)

 Attribution: By BruceBlaus (Own work) [CC BY-SA 4.0 (], via Wikimedia Commons

Attribution: By BruceBlaus (Own work) [CC BY-SA 4.0 (], via Wikimedia Commons

Having good vitamin D status increases the absorption of calcium by 30-50% and phosphorus by 80%. Not having enough vitamin D decreases the amount of calcium the body can use from food. This leads to an increase in parathyroid hormone (PTH) levels. Higher PTH levels help to maintain blood calcium levels by mobilizing calcium from bones, which weakens them, possibly to the extent of osteopenia and osteoporosis. Some signs and symptoms include aches and pains in bones and muscle, and a decrease in bone mineral density. (4)


Non-Bone Related Health Vitamin D Benefits

The vitamin D receptor can be found in almost all of the tissues and cells in the body. The binding of 1,25(OH)2D to the vitamin D receptor can stimulate various processes, such as decreased cellular proliferation, inhibiting angiogenesis, stimulating insulin production, and stimulating macrophage cathelicidin production. Vitamin D may regulate up to 200 genes that are associated with health benefits. (5)

Although some studies find different results, getting adequate vitamin D has been shown to likely prevent certain illnesses and diseases, including cancer. It was found to inhibit cancer cell growth and maturation. (1)

Those who consume a vitamin D3 daily dietary intake of more than 400 IU have been found to reduce their risk of cancer. (1)

One study found that children supplemented with 2000 IU during their first year of life had a 78% reduced risk of developing type 1 diabetes when they were checked 31 years later. Vitamin D also appears to have a strong role in maintaining blood pressure. Patients with hypertension who visited tanning beds and raised their 25(OH)D levels by more than 180% in 3 months became normotensive. In other words, their blood pressure normalized once they had adequate levels of vitamin D. (1)

Sunlight exposure helps treat tuberculosis, which is pretty cool. Macrophages who are infected with tuberculosis increased the production of vitamin D, as well as the expression of the vitamin D receptor. Together, these increase the protein cathelicidin, which is a bacteriocide and kills tuberculosis, as well as other infections. (1)

Vitamin D also appears to have a role in muscle strength, because muscle cells contain vitamin D receptors, and a deficiency is associated with muscle weakness.

Persons with bone and muscle pain symptoms may be misdiagnosed with fibromyalgia, arthritis, or chronic fatigue syndrome, when they actually might just need some vitamin D. (1)

Vitamin D receptors are also found on neurons and glia in the brain, and has many roles in brain processes, including brain development, neuroprotection, and neuroplasticity. Vitamin D is associated with depression. (7)


Not Many Foods Contain Vitamin D

Very few foods naturally contain vitamin D, and fortified foods don’t always contain enough to meet our needs. Fatty fish such as salmon and mackerel contain D3 and are the best choices to get vitamin D from food. Be sure to choose wild caught fish when possible. Wild caught salmon has between 500-1000 IU vitamin D per 100 g (3.5 ounces), and farmed salmon only contains 100-250 IU vitamin D per 100 g. (1)

Fatty fish like salmon, tuna, and mackerel, as well as fish and fish liver oils contain the most vitamin D, but the amount of vitamin D they contain can vary. Mushrooms sometimes provide vitamin D, especially if they are exposed to ultraviolet light in controlled environments. Some foods are also fortified with vitamin D, particularly milk. 1 cup of milk generally provides 100 IU of vitamin D. Butter, ice cream, orange juice, yogurt, margarine, and some other products are sometimes fortified with vitamin D as well.

Food Sources of Vitamin D (check labels, vitamin D amounts can vary) (3)


Vitamin D (IU)

Vitamin D (% Daily Value = 400 IU)

Cod liver oil, 1 tablespoon



Swordfish, 3 ounces



Salmon, 3 ounces



Tuna, canned, 3 ounces



Orange juice, fortified



Milk, fortified



Yogurt, fortified



Margarine, fortified, 1 tablespoon



Egg yolk, 1 large



Cereal, fortified




Vitamin D Supplementation

It’s likely that you’ll need to supplement during the colder months of the year. Serum 25-hydroxyvitamin D [25(OH)D] levels should be checked to determine vitamin D status. Vitamin D2 or vitamin D3 supplementation are both recommended, and supplementation of vitamin D has been shown to significantly reduce mortality. Many health care providers recommend 1000 IU daily, although that is a bit above the recommended dietary allowance. (5)

Many experts have come to the conclusion that in the absence of sunlight (UVB rays), 800-1000 IU of vitamin D should be taken daily. (1)

Its understood that D2 and D3 are both effective at raising serum 25(OH)D levels. However, D3 tends to be more effective at higher doses. (3)


Vitamin D is crucial for bone health, and likely to help with many illnesses and diseases, possibly reducing the risk of them. During the colder months (October-March), it’s a good idea to supplement with vitamin D, unless you are able to get enough vitamin D through diet. During the rest of the year (April-September) you should be able to get enough vitamin D from the sun. Getting outside 2-3 times a week for 30 minutes during the middle time of the day is best. If you’re shadow is longer than you are tall, its likely that you won’t be able to make vitamin D from the sun.