A.K.A. the sunshine vitamin, is technically a hormone, and classified as a non-essential fat-soluble vitamin because the body can produce it and uses fat to dissolve and store it.
Depending on where you live, it’s that time of year when our vitamin D levels drop because we have less sunshine during daylight savings time, we stay inside to avoid the cold, and the sun's UV rays are not strong enough for vitamin D production.
Vital Functions of Vitamin D:
- Key player in bone mineralization, important for bone growth and strength
- Maintaining the body’s use of calcium and phosphorus
- Helping maintain gastric secretions
- Bone metabolism and calcium maintenance
- Facilitating growth of soft tissues
- Bone calcification, growth, and repair
- Tooth formation
- Maintaining renal (kidney) and intestinal phosphate absorption
- Maintaining neuromuscular and immunity function
Production & Storage
The liver, cholesterol, skin, UV rays, digestion, fat, and kidneys all play a role in the production and transportation of active vitamin D3 a.k.a. 1,25-dihydroxyvitamin D3. The active form is the form our body needs and it is stored in the liver, bones, brain, and skin.
Vitamin D3 is produced in two ways:
- The precursor for active vitamin D3 is made in the liver from cholesterol and resides in the skin. When the skin is exposed to the sun’s ultraviolet light, the precursor is converted into pre-vitamin D3, which is eventually converted into the active form of D3.
- When foods are consumed that contain the inactive form of D3, it is also converted into the active form of D3.
Groups At Risk of Deficiency (not enough):
- Lack of vitamin D in the diet
- Dark skinned
- Severe liver and/or kidney disease
- Malabsorption issues (e.g. IBD, fat malabsorption)
- Inadequate sun exposure
- Taking medications that increase vitamin D needs
- Categorized as obese
- Greater than 70 yrs. old due to decreased production in the body as we age
- Breastfed infants, without formula or vitamin D supplementation
- History of gastric bypass surgery
- People living in areas of higher latitudes during the winter
Deficiency of Vitamin D Raises Risk For:
- Compromised bone health (e.g. osteoporosis, rickets, osteomalacia, high risk of fracture)
- Many varieties of cancer (e.g. colon, prostate, breast)
- Decreased muscle strength causing increased risk of falling
- Autoimmune disease (e.g. MS (multiple sclerosis), celiac disease, lupus, type 1 diabetes, lupus, IBD (inflammatory bowel disease), RA (rheumatoid arthritis))
- CVD (Cardiovascular disease) (e.g. hypertension)
- Renal (kidney) disease (e.g. CKD (chronic kidney disease))
- Diabetes (type 1 and 2)
- Glucose intolerance
- Mental health disorders (e.g. depression)
- Increased infection risk due to decreased immunity
Ultraviolet (UV) Sunlight (without sunscreen on skin):
- A very general estimate is that 20 minutes of exposure to UV rays to the face and arms would produce approximately 200 IU (international units)
- Typically, adequate vitamin D can be produced by exposing the face, arms, legs, or back, without sunscreen, to the sun for 5-30 minutes on a clear summer day during the hours of 10 a.m. and 3 p.m.
- Dark skinned people, will need to spend more time in the sun depending on how dark their skin is. One source stated that, in order to produce the same amounts of vitamin D, a fair skinned person would have to be in the sun for 30 minutes and the very dark skinned person would have to be in that same sun for 3 hours.
- According to Harvard Women’s Health Watch, if you live in the U.S. and are located in a latitude above the 37th parallel line, see picture below, the body can only produce the active form of vitamin D, via adequate UV rays, during the summer months.
Vitamin D Food Sources:
- Egg yolks
- Pink salmon
- Fatty fish (herring, salmon, sardines, halibut, mackerel )
- Cod liver and halibut liver oils
- Human milk
- Mushrooms (amounts vary by company, some expose them to UV light to increase the level of vitamin D)
Fortified (added to food, verify by reading the label)
- Milk, milk alternatives, and milk products such as yogurt
- Some cereals,
- Some cheese and butter
- Foods marked as fortified such as many protein bars, carbonated beverages, sports drinks, etc.
Vitamin D Supplements:
Because it is stored in the body, it is important to note that, when it comes to vitamin D, more is not necessarily better. This is because the body can easily reach toxic levels if the daily recommended or medically prescribed amounts are not properly followed.
Toxicity (too much) Vitamin D Raises Risk For:
- Elevated blood calcium (hypercalcemia)
- Elevated blood phosphorus (hyperphosphatemia)
- Decreased bone mineralization
- Calcification of soft tissues (calcinosis) such as kidney, lungs, heart, and the tympanic membrane of the ear.
- Kidney stones
- Excessive urination (polyuria)
- Excessive thirst (polydipsia)
- Nausea and vomiting
- Promotes bone calcium being returned to the blood, which causes high blood calcium
- Irreversible kidney damage
Vitamin D Status:
Once you calculate approximately how much vitamin D you’re consuming and/or producing in the sun daily, it is then recommended that you have a vitamin D blood test run, and, based on your results, your health care professional can tell you whether or not you need to take a supplement. Personally, this is how I handle my vitamin D status. For example, I just had it checked two weeks ago, it was low, so the doctor prescribed an increased amount for the next six months.
The recommended blood test to accurately determine your vitamin D status is the Serum 25-hydroxy vitamin D or 25(OH)D test. Each lab will supply the WNL (within normal limits) ranges for your results but a general recommendation, from WebMD, is that results of 20 to 50 nanograms/milliliter is WNL for healthy people and anything lower than 12 nanograms/milliliter is considered deficient. Notice it states healthy people.