Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. 5th ed. Belmont, CA: Wadsworth Cengage Learning; 2009.
Main roles of Vitamin D in the body:
1) Regulates Bone mineral metabolism
2) Regulates levels of Calcium within the blood
3) Cell differentiation (specialization), proliferation (multiplication) and growth
Dietary sources of Vitamin D:
1) Natural sources = beef, egg yolks, milk, cheese, butter, herring, salmon, tuna, sardines
2) Fortified sources* = yogurt, cheese, margarine, orange juice, bread, cereal
* Vitamin D fortification of these products is not mandatory and will depend on the manufacturer
Forms of Vitamin D:
1) Plants = ergosterol which is converted into ergocalciferol (D2) via irradiation (Typical supplement form)
2) Animals = 7-dehydrocholesterol which is converted into precholecalciferol via sunlight. Within 2-3 days precholecalciferol is converted into active form of cholecalciferol (D3)
Overview of Vitamin D Metabolism:
- Vitamin D3 is absorbed by micelles (lipid molecules) and transported to the intestine where it is absorbed and transported to the liver for activation into 25-OH D3. Liver makes alpha-2 globulin and Vitamin D- binding protein (DBP) also known as transcalciferin which are proteins that transport D3 into the blood
- Vitamin D can be stored within the skin, blood, muscles and adipose tissues
Vitamin D Roles within Individual Organs:
1) Intestine- Enhances calcium and phosphorus absorption
2) Kidney- Increases Calcium resorption from the bones to increase blood levels as needed
* Calcitriol (1,25-(OH)2D3) is the active form of Vitamin D in the kidney
* Increased Calcitriol production = Low blood Calcium; Parathyroid Hormone (PTH)
* Decreased Calcitriol production = high levels Vitamin D3 and increased Phosphorus intake
3) Bones- Increases Calcium absorption into the bones, and resorption from the bones to increase blood Calcium levels
4) Cells- Promotes cell differentiation; can inhibit abnormal cell growth in certain cancers
Possible Benefits of Adequate Vitamin D stores:
1) Decrease blood pressure by down regulating renin and angiotensin
2) Protects from autoimmune diseases such as Multiple Sclerosis, Type 1 Diabetes Mellitus, Rheumatoid Arthritis
3) Enhances Immunity
4) Increases Insulin Sensitivity
Signs/ Symptoms of Vitamin D Deficiency:
- In infants: seizures, growth retardation, decreased bone mineralization (rickets)
- In Adults: Low Calcium and Phosphorus absorption, which decreases bone density (osteomalacia); Low Calcium levels in the blood
Signs/Symptoms of Vitamin D Toxicity (levels > 7375 nmol/L)
1) Hypercalcemia (high calcium in the blood)
2) Anorexia
3) Nausea and Vomiting
4) Hypertension (high blood pressure)
5) Renal insufficiency
6) Failure to Thrive
7) Calcification of soft tissues
Exposure to sunlight can NOT lead to Vitamin D toxicity- the body will not synthesize Vitamin D when levels are adequate
Interaction of Vitamin D and Vitamin K:
Vitamin D is required to stimulate two Vitamin K dependent proteins as follows:
1) Osteocalcin = 15-20% non collagen protein in the bones
- Is dependent on Vitamin K carboxylation to bind Calcium thus playing a key role in bone remodeling and Calcium mobilization
2) MGP (Matrix Gla Protein)- Mobilization of Calcium; when deficient in MGP calcium can precipitate in arteries and soft tissues/organs
Weishaar T, Vergili JM. Vitamin D status is a Biological Determinant of Health Disparities. J Acad Nutr Diet. 2013; 113 (5): 643-651.
Skin color affects vitamin D synthesis from the sun. The darker the skin the longer a person must remain in direct sunlight to synthesize adequate levels of Vitamin D. Thus a non-Hispanic African American who has moved away from their ancestral home near the equator is often deficient in higher latitudes.
Institute of Medicine Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press; 2011.
| Age | RDA (ug/dl) | RDA (IU/dl) | UL |
| 0-6 mo | 10* | 400 | 1000 |
| 6-12 mo | 10* | 400 | 1520 |
| 1-3 yr | 15 | 600 | 2520 |
| 4-8 yr | 15 | 600 | 3000 |
| 9-70 yr | 15 | 600 | 4000 |
| >70 yr | 20 | 800 | 4000 |
RDA= Recommended Dietary Allowances; UL= Tolerable Upper Intake Level
* Measurements in infancy are Adequate Intakes (AI)
Au LE, Rogers GT, Hariss SS, Dwyer JT, et al. Associations of vitamin D Intake with 25-Hydroxyvitamin D in overweight and Racially/Ethnically Diverse US Children. J Acad Nutr Diet. 2013; Article in Press. Accessed September 2, 2013.
Vitamin D nutriture is identified as follows:
1) Inadequate = < 20 ng/ml
2) Adequate = 20 ng/ml - <30 ng/ml
3) Optimal = 30 ng/ml or greater
Risk factors for inadequate Vitamin D levels:
1) Tall
2) Heavy
3) Large waist circumference
4) Sedentary
It was found that dietary intake of high Vitamin D improved Vitamin D status.
Bischoff-Ferrari HA, Giovannucci E, Willett WC, Dietrich T, DawsonHughes B. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr. 2006;84(1):18-28.
Vitamin D nutriture is identified as follows:
1) Adequate = 30 ng/ml
3) Optimal = 36 ng/ml - 40 ng/ml
Strong Associations that Vitamin D:
1) Increases bone mineral density
2) Prevents bone fractures (intake of 700-800 IU Vitamin D daily might prevent 1/4 hip fractures)
3) Increases lower extremity function
4) Decreases falls
5) Enhances oral health/ Prevents periodontal disease
6) Decreases risks of colorectal cancers
Weak Associations Suggest that Vitamin D:
1) Prevents Multiple Sclerosis
2) Prevents Tuberculosis
3) Decreases insulin resistance
4) May prevent various Cancers
5) Prevents Osteoarthritis
6) Lowers blood pressure
Risk Factors for Deficiency:
1) Elderly
2) High latitudes
3) Obese
4) African American
Many populations may benefit or need seasonal supplementation in the winter.
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930.
- 25 Hydroxyvitamin D (25-(OH)D) is to be used as an indicator of Vitamin D level
- Deficiency is to be considered <20 ng/ml
- Insufficiency is to to considered 21-29 ng/ml
- RDA levels as currently set might be insufficient to meet all potential benefits of Vitamin D status in that Children may in reality need 1000 IU daily and Adults may need 1500-2000 IU daily.
- Obese children and adults taking medications such as anticonvulsant, glucocorticoids, antifungals and AIDS medications may need 2-3 times more vitamin D than the general population.
- Both D2 and D3 supplements are adequate to treat deficiency
To Treat Deficiency:
* 0-1 yr = 2,000 IU daily or 50,000 IU weekly X 6 weeks to be followed by maintenance dose of 400-1,000 IU daily
* 1-18 yr = 2,000 IU daily or 50,000 IU weekly X 6 weeks to be followed by maintenance dose of 600-1,000 IU daily
* 19+ yr = 6,000 IU daily or 50,000 IU weekly X 8 weeks to be followed by maintenance dose of 1,500-2,000 IU daily
* Obese/ Malabsorption syndromes/ Medication use = 6,000-10,000 IU to be followed by maintenance dose of 3,000-6,000 IU daily
Calcium and Phosphorus Metabolism:
1) When deficient in Vitamin D Calcium absorption = 10-15% which is increased to 30-40% with adequate Vitamin D levels
2) When deficient in Vitamin D Phosphorus absorption = 60% which is increased to 80% with adequate Vitamin D levels
Current studies continue to determine the role of Vitamin D in:
1) Inhibition of cell proliferation (multiplication) and induction of cell differentiation (specialization)
2) Inhibition of angiogenesis
3) Stimulation of insulin production
4) Inhibition of renin production
5) Stimulation of macrophage cathelicidin production
* Vitamin D regulates self and will inactivate when levels are too high
Causes of Deficiency:
1) Use of sunscreen- will decrease Vitamin D synthesis by 95% with SPF of 30
2) Darker skin- requires 3-5 times more exposure to sun
3) Obesity
4) Decreased dietary intake
5) Fat malabsorption syndromes
6) Nephrotic syndrome
7) Medications
Signs/Symptoms of Deficiency:
1) Altered phosphorus and Calcium levels
2) Decreased bone density (osteopenia and osteoporosis)
3) Rickets and Osteomalacia (bone pain/ muscle weakness)
* Supplementation likely necessary at latitudes > 33 degrees
*Do not supplement those with Chronic Granuloma Forming Disorder or Lymphoma
Target Vitamin D Levels:
1) 25(OH)D > 20 ng/ml = prevention of rickets and osteomalacia
2) 25(OH)D > 30 ng/ml = optimal level for bone health
3) 25(OH)D >30 ng/ml = possible reduction in risk of some cancers, autoimmune diseases, Type 2 Diabetes Mellitus, Cardiovascular Disease and infectious diseases
Wagner CL, Greer FR. Prevention of Rickets and Vitamin D Deficiency in Infants, Children and Adolescents. Pediatrics. 2008; 112: 1142.
Known Benefits of Vitamin D:
1) Bone Health
Possible Benefits of Vitamin D:
1) Decreased infections
2) Prevention of autoimmune diseases
3) Decreased rates of cancer
4) Reduction of Type 2 Diabetes Mellitus and possibly Type 1
Risk Factors
Darker skin (will need 5-10 times more sunlight exposure) and infants/children routinely protected from direct sun exposure.
Rationale and History of Routine Infant Vitamin D Supplementation:
- Supplementing maternal diet with 400 IU daily will raise levels in breastmilk to 25-78 IU, which is insufficient to meet infant needs of 400 IU.
- 400 IU suspected to be the minimal intake necessary to maintain Vitamin D stores sufficient to prevent Rickets
- In 2008 the American Academy of Pediatrics raised their recommendation to supplement all breastfed infants with 200 IU Vitamin D daily to 400 IU Vitamin D daily
- Supplementation to continue through adolescence when < 1 liter or equivalent intake of high Vitamin D foods to reach total intake of 400 IU is consumed
- Rickets has been identified in puberty
Additional notes and thoughts:
While going to school in a latitude of 41.7 degrees I had a Vitamin D level drawn on September 9 following summer vacation. My level was 31 with a fairly liberal exposure to sunlight. Many in the class was deficient.
Latitude values of interest:
- St. George, UT = 37.1
- Logan, UT = 41.7
- Los Angeles, CA = 33
- Atlanta, GA = 33
- Phoenix, AZ = 33
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