Nearly every tissue and cell in our body has a vitamin D receptor. Without enough activated vitamin D in the body, dietary calcium cannot be absorbed. Calcium is essential for signaling between brain cells, development of bone, and tooth formation. Let’s be honest, nobody likes rickets.
Studies also reveal that low vitamin D levels in the body are associated with:
- Increased loss of muscle strength and mass as we age
- Increased risk of cancers
- Lower levels of immunity
- Higher blood pressure
- The development of neurological disorders
- The development of diabetes
Alright, so we just spend more time in the sun or pop some supplements. Not so fast.
Despite the importance of vitamin D, it’s estimated that anywhere from 30% to 80% of the U.S. population is vitamin D deficient. It’s likely worse among people with darker skin living in northern zones, as their skin pigmentation screens out the relatively limited sunlight more effectively.
Vitamin D levels can also be affected by age and body fat levels. As we age, our ability to make vitamin D is reduced by 75%. Furthermore, vitamin D can get trapped in body fat, leading to a 55% reduction in blood levels for those who are over-fat.
Vitamin D isn’t really a “true” vitamin, as we don’t need food to attain it. Natural sunlight allows our body to create vitamin D and even destroys excessive amounts.
Think you’re soaking up vitamin D through office/car windows? Wrong. Glass blocks virtually all UVB, preventing vitamin D from being made.
And sunscreen is similar. Applying sunscreen with an SPF of 15 will decrease the amount of vitamin D made in the body by about 99%. Hooray for basal cell carcinoma prevention. But bummer for vitamin D production.
Activated vitamin D has a serum half life of 2-3 weeks and its production in the skin is limited to 10,000-20,000 IU each day. Spending 20 minutes riding your bike outside in the summer sun produces 100 times more vitamin D than government agencies say you need. And once serum levels reach 150 nmol/L, any excess is inactivated. Thanks be to Mother Nature.
Vitamin D is extremely rare in foods. It’s found in fish, cod liver oil, mushrooms, liver and eggs – but usually not in substantial amounts (except in cod liver oil).
Farmed varieties of fish contain very little vitamin D compared to the wild varieties. The only reason we even get vitamin D from foods like milk and cereal is because these foods are fortified with it — it doesn’t naturally occur.
Breast milk contains low amounts, with about 25 IU per liter.
Thus, getting enough vitamin D from whole foods is virtually impossible; it truly is the sunlight vitamin.
Fortification studies in adults show that consuming 100 – 1000 IU of vitamin D each day results in increased blood concentrations by 15 to 40 nmol/L. Other data with supplements indicate that for every 100 IU of vitamin D we ingest, we raise our blood levels by 2.5 nmol/L.
What intake is optimal?
An intake of greater than or equal to about 1000 IU may be needed for most of the population. For postmenopausal women and older men, 25(OH)D concentrations of less than 30 to 80 nmol/L are associated with negative health outcomes.
For infants at northern latitudes, studies suggest that 200 IU vitamin D2 per day may not be enough to prevent vitamin D deficiency. A meta-analysis in adults suggested that an increased intake of vitamin D3 of 100 IU per day was associated with an increase in circulating concentration of 25(OH)D of 1 to 2 nmol/L. A recent study on women in Maine found that 800 IU of vitamin D per day was enough to reach and maintain adequate blood levels during the winter (for most of the women).
Taking very high daily doses of vitamin D—for example, 50 or more times the recommended daily allowance (RDA)—over several months can cause toxicity and a high calcium level in the blood (hypercalcemia).
Early symptoms are loss of appetite, nausea, and vomiting, followed by excessive thirst, weakness, nervousness, and high blood pressure. Because the calcium level is high, calcium may be deposited throughout the body, particularly in the kidneys, blood vessels, lungs, and heart. The kidneys may be permanently damaged and malfunction, resulting in kidney failure.
Some studies suggest that intakes up to 10,000 IU per day have not been associated with adverse effects. If you take more than 10,000 IU per day of vitamin D orally for more than 6 months, you are definitely at risk of becoming vitamin D intoxicated. And remember, we cannot become vitamin D intoxicated from excessive sunlight.
Summary and recommendations
Vitamin D deficiency is a disease of neglect. It’s up to us to get in the sun and/or use a supplement as needed. And the data seem to be pointing towards reaching “optimal” levels, not just “normal” levels.
The only way to know for sure if you have a vitamin D deficiency is to get a blood test, which you can get through your family doctor.
Most experts agree that having a blood level of:
• 30-50 nmol/L (12-20 ng/mL) of • <30 nmol/L (12 ng/mL) of 25(OH)D 25-hydroxyvitamin D3, or 25(OH)D is considered a severe deficiency is insufficient for optimal health
Ideally, in order to optimize bone health and minimize the risk of disease, you want to achieve a blood level of vitamin D of 50-100 nmol/L (20-40 ng/mL).5
Work with your doctor to figure out if you need to supplement, and if so, what dose to take, and for how long.
SOURCE TAKEN FROM PRECISION NUTRITION.