NEWSLETTER
Vitamin D: Are we living in an Epidemic of Vitamin D deficiency
S. Abbas Raza — Consultant Endocrinologist Shaukat Khanum Hospital and Research Center
Why Vitamin D Important and what are its Physiologic functions?
Vitamin D maintains calcium homeostasis, maximizes intestinal absorption of calcium (In vitamin D-sufficient people: 30% of calcium is absorbed from the diet while in vitamin D-deficient people: 10-15% of calcium is absorbed from the diet), maintains phosphate homeostasis. Vitamin D Deficiency results in increased production and excretion of PTH (parathyroid hormone) or secondary hyperparathyroidism.
Vitamin D plays its role in musculoskeletal as well as extraskeletal organs. Musculoskeletal Effects include maintenance of normal musculoskeletal function (Skeletal muscle has receptors (VDR) for 1, 25(OH) 2D3, Severe vitamin D deficiency is associated with muscle weakness, limb pain & impaired physical function).
Secondary hyperparathyroidism, associated with Vitamin D Deficiency, causes an increase in bone resorption (calcium released from bone) and may precipitate or exacerbate osteoporosis. In more severe vitamin D deficiency, secondary hyperparathyroidism & low calcium X phosphate product increases unmineralized osteoid leading to Osteomalacia in adults and Rickets in children.
Extraskeletal Effects of Vitamin D include regulation of cell growth and effects on immune function. Epidemiologic studies have shown that living at lower latitudes is associated with a decreased risk of many chronic diseases including multiple sclerosis, hypertension, and cancer of the colon, breast, and prostate. Since the production of vitamin D is more efficient at lower latitudes, this may explain these interesting findings. Some studies have shown that increasing vitamin D intake decreases the risk of certain chronic diseases like rheumatoid arthritis, hypertension, and colon cancer.
Apart from the above mentioned disorders, interestingly there are quite a few recent studies which relate Vitamin D status with D.M type 2 as well as D.M Type 1, Growth retardation/Short stature (Effect on IGF-1) and other disorders.
What are the sources of Vitamin D and how is it metabolized?
Vitamin D is found in two form Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). There are number of metabolites and analogues of these substances available. Vitamin D is found in Precursor form (sometimes referred to as a “prohormone”) and it must be metabolized to become biologically active which is called Calcitriol.
Should it be called a “Vitamone” rather then a Vitamin??
Although called a vitamin, but vitamins must be provided from the diet because they can’t be synthesized or the rate of synthesis is not sufficient to maintain health and they are necessary in small amounts for normal metabolic functioning. But Vitamin D acts more like a hormone, as hormones are compounds produced in one part of the body and transported to another part of the body where they exert a specific regulatory or functional effect. Characteristics of Vitamin D consistent with hormonal functions include that it is synthesized in skin, transported in blood to distant sites to exert its action, activated by a tightly regulated enzyme, active form binds to specific receptors in target tissues and receptors are found in many cells throughout the body.
Is Vitamin D deficiency a Myth or a reality??
Vitamin D inadequacy has been reported in approximately 36% of otherwise healthy young adults and up to 57% of general medicine inpatients in the United States and in even higher percentages in Europe. There are some astonishing figures which have come out from subcontinent. Study published by Atiq et al revealed 48% nursing mothers and 52% infants had levels less than 25 nmol/ L. Studies done in India reveal similar prevalence of vitamin D deficiency. Dr. Alok Sachen et all published their observation in which eighty-four percent of women (84.3% of urban and 83.6% of rural women) had 25(OH) D values below 22.5. Recent work from Zargar et all reveals a very high prevalence (83%) of vitamin D deficiency (defined as a serum 25 (OH) D concentration of 50 nmol/l) in apparently healthy adults from Kashmir. These studies support the earlier observation, hence signifying the gravity of Vitamin D deficiency in this part of the world
How to determine Vitamin D status and what is the optimal level of Vitamin D?
Serum 25(OH) D3 is major circulating form of vitamin D and also best indicator of vitamin D status. It reflects production from sunlight exposure and dietary intake. Its half-life approximately 2 weeks and expressed as ng/mL or nmol/L, where 1 ng/mL 25(OH) D3 ~ 2.5nmol/L 25(OH) D3. Usually vitamin D insufficiency is considered at 10–30 ng/mL (~ 25-75 nmol/L) and
Vitamin D Deficiency at < 10 ng/mL (~ 25 nmol/L). But these numbers could vary according to reference range in different Lab. Vitamin D (25-hydroxyvitamin D) levels 30 ng/ml are required to maintain maximum bone and cellular health, while levels < 30 ng/ml cause suboptimal calcium absorption and increase in PTH secretion.
What is the etiology of Vitamin D Deficiency?
Factors which result in Vitamin D deficiency include inadequate sun exposure, inadequate dietary intake, Aging, Co-morbid conditions and Drug interactions. Inadequate sun exposure results from living at higher Latitude, in winter (November-February), with more oblique zenith angle of the sun and type of Skin. Inadequate dietary intakes is a major contributor to Vitamin D deficiency in Pakistan as foods are generally not enriched with vitamins. Other reason include inadequate consumption of food rich in Vitamin D such as Fish liver oils (e.g. cod liver oil), salmon, mackerel, sardines, liver and fat of aquatic mammals, Eggs (from hens fed Vitamin D) and fortified foods (milk, orange juice, cereal and infant formulas). Vitamin D deficiency related to Aging is multifactorial, which included decreased ability to produce vitamin D3, Increased incidence of lactose intolerance, Decreased renal function, ability to convert 25(OH)D3 to 1,25(OH)2D3 and may be housebound or institutionalized/minimal exposure to sunlight. Other Co-morbid conditions leading to deficiency include malabsorption (in Crohn’s disease, Whipple’s disease and Sprue), severe liver failure and obesity. Drug interactions result in impaired vitamin D absorption (Mineral oil laxatives, Obesity management medication – Orlistat, Bile acid sequestrants – Cholestyramine and Colestipol), may increase vitamin D catabolism (anticonvulsants, cimetidine, thiazides) and some fat substitutes may also decrease vitamin D absorption (Olestra-Not available in Pakistan).
How to replace or maintain Vitamin D levels?
Historically, adequate Intake (AI) of vitamin D for males & females was recommended to be for Infants till 50 years: 200 IU/day (5 mcg/day), ages 51-70 years: 400 IU/day (10 mcg/day) and = 71 years: 600 IU/day (15 mcg/day). But recent information suggests that this is too low of daily intake and if these recommendations are followed they do not result in normalizing vitamin D levels in body. Hence higher dosage is suggested by all the experts of this field. This varies any where from 1000 IU daily to 2000 IU daily. Even higher doses may be required for people with certain medical condition such as chronic Steroid use.