Everything you wanted to know about Vitamin D

By Nigel Kinbrum aka MuscleTalk member nigeepoo

Vitamin D is known as the 'Sunshine Vitamin'. It was once thought that a deficiency in it was rare and that it was only involved in calcium homeostasis in bones, and that a lack of it only caused the conditions rickets in children or osteomalacia in adults. Recent research however, has shown that not only is vitamin D involved in a whole host of bodily processes but that a deficiency in it may actually be very common, leading to a whole host of degenerative diseases.

What is Vitamin D?
Is a group of fat-soluble prohormones the two major forms of which are vitamin D2 (Ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D also includes metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to ultraviolet B radiation from sunlight. As a prohormone, vitamin D has no hormone activity itself, but is converted to the active hormone 1,25(OH)-D3 through a tightly regulated synthesis mechanism. For types see here.

How common is Vitamin D deficiency?
According to Hyppönen & Power, in a large sample of the white British population born in 1958, 60.9% of subjects had serum 25(OH)D (the active metabolite of Vitamin D) of <75nmol/L in summer and autumn, and 87.1% had serum 25(OH)D of <75nmol/L in winter and spring.

Here's my experience of vitamin D: For many years, I was struggling to cope with my job and I eventually took early retirement on the grounds of ill-health. In mid-2006 I was given a serum 25(OH)D test and the result was 73nmol/l. As the Reference Range for serum 25(OH)D is 33.1-129 nmol/l, I was technically not deficient in vitamin D. Subsequent events suggest otherwise.

In January 2007, after reading the above study and a study by Vieth, Kimball, Hu & Walfish, I began to supplement with 2,000 iu/day of vitamin D3 and also used a UVB+IR lamp for 3 minutes each night. At first, nothing happened and I was pretty sceptical about getting any improvement. However, after about 8 weeks, I began to notice an awakening in my brain. This continued, and by March 2007, I was feeling quite perky. Friends commented on the fact that I was becoming very chatty and I was also waking early in the morning raring to go, totally unlike my former self. In May 2007, I had another serum 25(OH)D test and the result was 115nmol/l. Another interesting result was my serum triglycerides, something that is usually always higher than is desirable. My serum TG was 1.4mmol/l (reference range <1.8mmol/l). This was the lowest result since tests began in 2002.

I began to get bored with standing around stark naked in front of a UV lamp for 3 minutes each night and stopped doing this. Slowly, my brain began to go back to sleep. I couldn't understand why as I thought that 2,000 iu/day of Vitamin D3 (10 x RDA) was more than enough. In November 2007, I had another serum 25(OH)D test. When I saw my endocrinologist in December 2007, I was quite shocked to see that the result was now 70nmol/l. I immediately increased my vitamin D3 intake to 5,000 iu/day (25 x RDA) and within two weeks, my brain started to wake up again. I will be having another blood test in May 2008.

See also The urgent need to recommend an intake of vitamin D that is effective.

What foods contain it?
For a list of foods high in vitamin D, see here. Beware of foods that have been 'fortified vitamin D', as vitamin D2 may have been used. This is much less effective than vitamin D3 according to Armas, Hollis & Heaney. Vegetarians and vegans may not want to eat foods containing vitamin D3 as this is sourced from animals (e.g. the lanolin from a sheep's coat). Eating the Standard English diet, it is difficult to obtain 5,000 iu/day of vitamin D. The cheapest way to get a lot of it is by going out in the sun in a swimsuit for 20 or so minutes in the middle of the day in summer & autumn, which costs absolutely nothing! As vitamin D is fat-soluble, the body can build up stores of the stuff to keep you supplied over winter and spring.

Vitamin D Deficiency, Insulin Resistance and The Metabolic Syndrome/Type 2 Diabetes
According to Hyppönen & Power, there is a strong association between decreasing 25(OH)D, increasing Body Mass Index (BMI) and increasing HbA1c (glycosylated haemoglobin – a marker for blood sugar control). Increasing HbA1c is associated with increasing relative risk (RR) of mortality, according to Khaw, Wareham, Bingham, Luben, Welch & Day, summarised here.

According to Chiu, Chu, Go & Saad, there is a positive correlation of 25(OH)D concentration with insulin sensitivity and a negative effect of hypovitaminosis D (low levels of vitamin D) on pancreatic ß-cell function. Subjects with hypovitaminosis D are at higher RR of insulin resistance and the Metabolic Syndrome.

Vitamin D Deficiency and Cancer
According to Lappe, Travers-Gustafson, Davies, Recker & Heaney, subjects receiving 1400–1500mg/day supplemental calcium and 1100 iu/day supplemental vitamin D3 had a RR of getting any type of cancer of 0.402 which is equivalent to a 60% reduction in the risk of getting cancer compared to the non-supplementing group. If the first 12 months results were discarded (to exclude any subjects who already had cancer when they started the study), the RR was 0.232 which is equivalent to a 77% reduction in the risk of getting cancer. One wonders what the results would have been if 5,000 iu/day of vitamin D3 had been used. See also Díaz, Paraskeva1, Thomas, Binderup & Hague.

Vitamin D Deficiency and Mental Function
According to Vieth, Kimball, Hu & Walfish as mentioned above, supplementing with 4,000iu/day of vitamin D3 produced a huge reduction in the so called 'miserableness factor' without affecting serum calcium levels. According to Wilkins, Sheline, Roe, Birge & Morris, vitamin D deficiency was associated with low mood and worse cognitive performance in older adults. According to Gloth, Alam & Hollis, improvement in 25(OH)D was significantly associated with improvement in depression scale scores.

Vitamin D Deficiency and Blood Pressure
According to Forman, Giovannucci, Holmes, Bischoff-Ferrari, Tworoger, Willett & Curhan, plasma 25(OH)D levels are inversely associated with the risk of incident hypertension.

Vitamin D Deficiency and the Immune System
According to Cannell, Vieth, Umhau, Holick, Grant, Madronich, Garland & Giovannucci, vitamin D deficiency predisposes children to respiratory infections. Ginanjar, Sumariyono, Setiati & Setiyohadi, The active form of vitamin D produces and maintains self immunologic tolerance.

Vitamin D Deficiency and Falls
According to Dharmarajan, Akula, Kuppachi & Norkus, in the pilot study of older adults with gait imbalance and falls, vitamin D deficiency (< 20ng/mL) was observed in 54% of patients tested and previously unrecognised.

Vitamin D Deficiency and Chronic Pain
According to Plotnikoff & Quigley, all patients with persistent, non-specific musculoskeletal pain are at high risk of the consequences of unrecognized and untreated severe hypovitaminosis D. According to Al Faraj & Al Mutairi, vitamin D deficiency is a major contributor to chronic low back pain in areas where vitamin D deficiency is endemic. According to Gloth, Lindsay, Zelesnick & Greenough, there may be a pain syndrome associated with vitamin D depletion that appears as hyperaesthesia worsened by light, superficial pressure or even small increments of movement.

But doesn't the sun damage the skin and cause skin cancer?
Inappropriate sun exposure can certainly damage the skin. Chronic overexposure to sun (e.g. farmers and other outdoor workers) causes wrinkly, leathery skin and may be involved in the development of skin cancers such as Basal Cell Carcinoma and Squamous Cell Carcinoma. These skin cancers are easily removed and rarely fatal. However, acute overexposure to sun (e.g. people getting severe sunburn on foreign holidays and those over-enthusiastic on being tanned) causes the much more serious Malignant Melanoma. This condition, if not caught early enough, has a very high risk of mortality. However, sensible sun exposure may have more benefits than hazards. See Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers: vitamin D as a possible explanation.

Is it possible to get too much Vitamin D?
It is possible to over-supplement with vitamin D. According to Vieth, published cases of vitamin D toxicity with hypocalcaemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intakes of >1000µg/day (>40,000 IU)/d. People suffering from sarcoidosis, primary hyperparathyroidism, a history of calcium oxalate kidney stones and Milk-Alkali Syndrome need to be careful with their vitamin D intake. People prescribed the drug Warfarin also have to be careful, as Warfarin is a vitamin K antagonist which can result in calcification of tissues.

However, it is not possible to overdose on vitamin D by sun exposure as the metabolic processes down-regulate when ~10,000iu has been produced. To find out when the sun is strong enough to produce vitamin D in your skin, see the Vitamin D Synthesis in Human Skin Calculator.