What is vitamin D?
First and foremost, vitamin D is a prohormone, meaning it is classed as a ‘chemical messenger’ that can be sent to other parts of the body for specific tissue and body system functions via the blood. It is a fat soluable vitamin, meaning it can dissolve in fats and oils. This also means it can be stored in the body’s adipose (fat) tissue and the liver. Vitamin D toxicity is possible due to its ability to be stored in the body. Normal, healthy levels of vitamin D are considered to be at between 20ng/ml to 50ng/ml. Initially, there are two forms of vitamin D that are obtained from direct sun exposure to the skin and in certain foods that we eat. These are D2 (ergocalciferol) and D3 (cholecalciferol). These are considered to be biologically inactive until they go through two enzymatic hydroxylation reactions in firstly the liver and finally the kidneys. The end result is the biologically active hormone, calcitriol (1,25-dihydroxyvitamin D).(1)
Benefits of vitamin D
Emerging research supports the possible role of vitamin D against cancer, heart disease, fractures and falls, autoimmune diseases, influenza, type-2 diabetes and depression. (1)
Biologically activated vitamin D (calcitriol) facilitates a higher percentage of the intestinal absorption of calcium and phosphorus. This helps with bone mineralization, important for bone growth and bone strengthening. Prolonged poor levels of vitamin D in children can result in rickets, a softening of bones during development. Similarly, osteomalacia can cause developing bones to bow, and fractures in older adults, due to lack of vitamin D. Osteoporosis is a chronic bone disease that effects older adults where the bone density declines over time due to low calcium intake. Vitamin D may help enrich calcium absorption to help slow the degradation of bone density, however, most people only find out they have osteoporosis after they have Brocken a bone later in life. More health services are recommending testing for vitamin D deficiencies for earlier treatments of these chronic bone diseases.
Vitamin D decreases cell proliferation and increases cell differentiation, stops growth of new blood vessels and has anti-inflammatory effects. Studies have suggested a link between low levels of vitamin D and increased risk of cancer with the strongest evidence shown for colorectal cancer. Follow up studies have found subjects with high concentrations of Vitamin D were half as likely to be diagnosed with colon cancer than those with low vitamin D concentrations. (2) A definitive conclusion is yet to be made between vitamin D concentration and cancer risk.
Studies are providing evidence that vitamin D has a beneficial role in lowering risk of heart disease via the renin-angiotensin hormone system, suppression of inflammation or directly on the cells of heart and blood vessel walls. In a separate study, patients with low vitamin D were three times more likely to be diagnosed with hypertension, a significant risk factor for cardio vascular disease. (3)
In a randomized controlled trial study in 2007on the effects of calcium and vitamin D supplementation on blood glucose and inflammation in nondiabetic adults, the results were interesting and recommendations made for further trials. 314 adults without diabetes received calcium citrate and vitamin D supplements or placebos daily for 3 years, measuring fasting plasma glucose (FPG) and insulin sensitivity were measured at baseline and 3 years. It was found that participants with impaired fasting glucose (FPG 5.6-6.9 mmol/l) that were taking the supplements had a lower rise in FPG at 3 years, concluding that vitamin D and calcium citrate may attenuate increases in glycemia and insulin resistance over time. (4)
A study on the effects of vitamin D supplementation on the development of type 1 diabetes in infants born in 1966 was carried out in northern Finland. 10821 children were followed up after 1 year and data collected about frequency and dose of vitamin D supplementation. The primary outcome measure was diagnosis of type 1 diabetes by end of December 1997. 81 were diagnosed with diabetes during the study. Vitamin D supplementation was associated with a decreased frequency of type 1 diabetes. (5)
A 4 month randomized, double-blind, placebo-controlled trial compared vitamin D(3) supplements with placebo and its effects on the incidents of influenza A in school children. Influenza A occurred in 10.8% of children in the vitamin D group compared with 18.6% of children in the placebo group. (6)
As mentioned before, one of the best sources of vitamin D come from direct sunlight on the skin. Dietary vitamin D sources include salmon, herring, sardines, cod liver oil, canned tuna, egg yolks, mushrooms and fortified foods such as some milks, orange juice and some cereals. (7)
There are increasing findings through studies about correlations between specific levels of vitamin D and better health outcomes. Most of these studies suggest more trials and studies need to be conducted to bolster the positive findings made so far. The emerging benefits of vitamin D are certainly an exciting subject, and I will be continuing my research in this area.