Are you getting enough vitamin D?
I’m often asked for my opinion, or to give advice, on taking supplements. Mostly from people opposed to taking conventional medicines. The truth is, I don’t really know enough about nutrition to give advice.
However, I recently read a review ‘Vitamin D in health and disease: Current perspectives’, (Zhang and Naughton, 2010), and was so taken aback by what I read that I thought I should review their review and outline the key aspects relating to vitamin D deficiency.
Vitamin D is essential for the absorption of calcium. The two precursors to Vitamin D are, Vitamin D3 which is formed when the skin is exposed to sunlight (UVB), and Vitamin D2 which enters circulation through the diet.
These two precursors (D2 and D3) are converted to vitamin D [25(OH)D] by the liver. Vitamin D [25(OH)D] is the major circulating form of vitamin D that is used to determine vitamin D levels in the body.
Oily fish such as salmon, mackerel, and sardines are rich in vitamin D3. Egg yolks contain vitamin D, though the amounts are highly variable, and a small number of foods such as milk, orange juice, bread and cereals are fortified with vitamin D.
Vitamin D Deficiency Occurs when people either do not have an appropriate dietary intake, do not have adequate exposure to UVB rays, or have a medical condition that prevents them from processing adequate amounts of vitamin D. Vitamin D deficiency is defined as a level of <20 ng/ml (50 nmol/l).
In 1997, the US Institute of Medicine recommended a daily intake of vitamin D of 200-600 IU. (IU refers to international units, which equals 25 ng). Many studies since, have revealed that without adequate sun exposure, children and adults actually require 800-1000 IU/day.
Vitamin D deficiency can generally be divided into two subgroups: UVB-related deficiency (Sun) and condition-related deficiency (Diet).
7-dehydrocholesterol is essential for the synthesis of vitamin D from UVB. The elderly have decreased levels of 7-dehydrocholesterol and are therefore particularly at risk of vitamin D deficiency. Sunscreens also dramatically reduce the interaction of UVB with 7-dehydrocholesterol. A sunscreen with a sun protection factor of 8 reduces the production of D3 by 95%!
Dark skin people are also at greater risk as they have large amounts of melanin in their skin which competes with 7-dehydrocholesterol for absorption of UVB. A person with dark skin requires 10-50 times more exposure to sunlight to produce the same amount of vitamin D.
Condition-related deficiency Vitamin D requires the presence of dietary fat in the gut for absorption. Certain conditions, such as Crohn’s disease, cystic fibrosis and celiac disease are associated with fat malabsorption and thus may lead to vitamin D deficiency.
In addition, some anticonvulsant drugs used to treat epilepsy and bipolar disorder can result in destruction of vitamin D and people with chronic kidney disease may be unable to make sufficient vitamin D.
Disease Management and Prevention.
Osteoporosis Vitamin D deficiency is associated with a marked decrease in Calcium absorption. Approximately 33% of women aged 60-70 and 66% of those over 80 have osteoporosis, increasing the risk of fractures, the consequences of which can be severe. 15-25% of patients with a hip fracture require long term nursing home care, and 10-20% die within 1 year.
Trials using 700-800 IU/day vitamin D found a 26% reduction in risk of sustaining a hip fracture. A French study of over 3000 elderly women found that calcium (1200 mg/day) and vitamin D (800 IU/day) reduced the probability of hip fractures by 43%.
Over 90% of hip fractures result from a fall. Muscle weakness is a prominent feature of vitamin D deficiency. In a 5-month trial, elderly people received 800 IU/day of vitamin D plus calcium and exhibited a 72% reduction in the risk of falls. In another trial, 700 IU/day of vitamin D plus 500 mg of calcium in 246 community-dwelling women showed a 46% reduction in falls.
Hypertension Millions of people are affected by high blood pressure worldwide. An 8-week study of 148 vitamin D deficient elderly women demonstrated a 9% decrease in blood pressure with 800 IU/day vitamin D. In another study, patients with hypertension received UVB radiation three times a week for 3 months and showed a 6 mm Hg reduction in blood pressure.
Multiple sclerosis (MS) MS is more common in temperate climates than in the tropics and studies have shown that individuals with MS tend to have insufficient vitamin D levels. One hypotheses is that the increase of vitamin D from sunlight exerts a protective effect. Although only a few reports are available on the use of vitamin D in treating MS patients, positive results from animal studies suggests that vitamin D supplementation could potentially improve the symptoms of MS. Vitamin D has also been shown to have effects in preventing MS. One study revealed that women who used vitamin D (>400 IU/day) had a 40% lower risk of developing the disease.
Cancer The first study indicating that sunlight exposure may lower the risk of cancer was almost seven decades ago. More recently, several studies have found a link between an increased risk of certain types of cancer and vitamin D deficiency.
Rheumatoid Arthritis (RA) Studies show that vitamin D has the ability to suppress the development of autoimmunity in animal experiments although the association of vitamin D intake and RA in humans has not been well studied. One study of 30,000 women, did however, observe an inverse association between greater intake of vitamin D and RA risk.
Diabetes A diabetic epidemic has emerged during the 20th century. Vitamin D deficiency inhibits pancreatic secretion of insulin, resulting in impaired glucose tolerance. A study of over 80,000 women showed that a combined daily intake of >1200 mg calcium and >800 IU/day vitamin D was associated with 33% lower risk of type 2 diabetes. Another study, of over 10,000 children over 31 years, indicated that 2000 IU/day of vitamin D, during their first year of life, reduced the risk of type 1 diabetes by ~80%.
Conclusion Vitamin D inadequacy is a global problem. In the USA, approximately 36% of otherwise healthy adults suffer from vitamin D deficiency and these figures are even higher in Europe.
The link between vitamin D deficiency and osteoporosis is well established. The association with other disorders, including hypertension, multiple sclerosis, cancer, rheumatoid arthritis and diabetes is less robust and requires further research.
If you are going to supplement your vitamin D intake, studies suggest that (800–1000 IU/day) is required in order to have any real preventative or treatment effect.
I’m not a dietitian and so will not offer advice. What I can say, is that despite never taking supplements before, since reading this paper, I have started taking 800 IU/day vitamin D supplements.
For references and to read the entire article please click on the link below: http://www.biomedcentral.com/content/pdf/1475-2891-9-65.pdf