MICROgenics^® Vitamin D 1000IU

Vitamin D metabolism

Vitamin D3 (cholecalciferol) is a steroid-derived hormone made naturally in the skin when exposed to solar ultraviolet B (UVB) radiation of 290–315 nm wavelength, which is within the spectrum that causes sunburn. One full body exposure to UVB can create the same amount of vitamin D as an oral intake of 250 mcg (10,000 IU).¹

When skin is exposed to UVB, a cholesterol metabolite, 7-dehydrocholesterol, is converted to previtamin D3, which then undergoes thermal isomerisation to form vitamin D3. It is transported to the liver, where it is converted to 25-hydroxycholecalciferol (25(OH)D), which is then converted to the active form, 1,25 dihydroxycholecalciferol (1,25(OH)2D), in the kidneys by the action of parathyroid hormone. This process of making active vitamin D can also occur in other tissues.

Vitamin D deficiency is a common health issue

Vitamin D deficiency is becoming more common because exposure to sunlight is restricted by indoor lifestyles, excessive clothing, and sunscreen use. At latitudes above 35º, the angle of the sun is so oblique in winter that UVB radiation below 315nm wavelength is absorbed by the ozone layer, preventing it reaching the skin.¹ Individuals with dark skin require 10-50 times the exposure to UVB to make vitamin D compared to individuals with light skin.¹ A factor 8 or 15 sunscreen, properly applied, reduces the skin’s ability to make vitamin D by 95 and 99% respectively.² Ageing reduces the amount of 7-dehydrocholesterol in the skin and substantially impairs vitamin D synthesis.¹

Vitamin D deficiency is more common in Australia and New Zealand than previously believed. Dietary intake of vitamin D and sun exposure are inadequate in Australia and low vitamin D status is common over a wide latitude range, with a study finding behavioural factors more important than seasonal factors.³ A Queensland study found that 42.5% of subjects had low blood levels of vitamin D at the end of winter.⁴ Deficiencies are more common in dark-skinned veiled pregnant women, mothers of infants treated for rickets, and elderly nursing home and hostel residents.⁵ Australian studies have found marginal deficiencies in 23% and 43% of younger adults.⁵

Most foods are poor sources of vitamin D. Richest sources are fatty fish, shellfish, meat, milk, eggs, butter, cream, and fortified foods such as fortified milk and margarine but the amount of dietary vitamin D is extremely low compared to the amount normally made in the skin. Fish liver oils are a useful vitamin D supplement but may provide more vitamin A than is desirable.

Vitamin D strengthens bones

Calcium and phosphate as hydroxyapatite provide rigidity and strength in bones. When blood levels of calcium drop, parathyroid hormone is released and stimulates the kidneys to produce 1,25(OH)2D. This causes calcium to move out of bones into the blood, increases calcium absorption from foods and reduces losses in urine to ensure blood levels of calcium are adequate for normal heart, muscle and nerve function. When blood levels of calcium are restored, bone is rebuilt.

Inadequate vitamin D status is implicated in osteoporosis, the common bone-weakening condition affecting Australians. A low calcium intake and inadequate vitamin D weakens bones over time. Older people make less vitamin D and absorb less dietary calcium because their intestines are no longer as responsive to active vitamin D and this can be compensated for by increased calcium intake and maintaining adequate levels of vitamin D.⁶

An Australian meta-analysis of trials that used calcium or calcium with vitamin D found that a minimum of 1200 mg of calcium and 800 IU of vitamin D was effective for prevention of osteoporosis in older people.⁷ The meta-analysis reported that calcium and calcium in combination with vitamin D was associated with a 12% reduction in risk. In 23 studies, calcium and calcium with vitamin D reduced bone loss in the hip and spine. The researchers warned that many formulations on the market contain too little calcium and vitamin D to provide an effective dose.

A 5-year Australian study of 120 elderly community-dwelling women found that 1200 mg a day of calcium with 1000 IU a day of vitamin D lowered parathyroid hormone levels and maintained bone mineral density of the hip at year three and five.⁸ A meta-analysis of clinical trials concluded that vitamin D supplements reduced the risk of spinal fractures by about 37%, in part because of improved muscle strength and reduced risk of falls.⁹ A more recent review concluded that taking 700-800 IU a day of vitamin D reduces the risk of hip and non-vertebral fractures in elderly people but 400 IU a day is insufficient.¹⁰ In patients with knee osteoarthritis, 66% were low in vitamin D and low serum 25(OH)D correlated with reduced bone mineral density.¹

Vitamin D strengthens muscles

Vitamin D maintains calcium supply to muscles for contraction and a deficiency causes muscle weakness and pain. In a US study of patients with persistent non-specific musculoskeletal pain, 93% were found to have low serum levels of 25(OH)D.¹² An Egyptian study found that 81% of women with low back pain were deficient in vitamin D13 and a study of veiled teenagers in the Netherlands found that vitamin D deficiency was implicated in limb-girdle myopathy that rapidly resolved on Vitamin D supplementation.¹⁴ A low 25(OH)D level in elderly Swedish women was associated with poor physical activity level, impaired gait speed and balance.¹⁵ A study of elderly people in the Netherlands found that almost half had below normal serum 25(OH)D and this was associated with poorer physical performance.¹⁶ A meta-analysis found that Vitamin D supplementation in elderly people reduces the risk of falls by more than 20%, compared with those on calcium or placebo.¹⁷

Vitamin D assists immunity

Active vitamin D can modulate immune activity by preventing excessive expression of inflammatory cytokines and increasing the capacity of macrophages to release an 'oxidative burst' that destroys pathogens.¹⁸ It stimulates the production of potent anti-microbial peptides in immune cells, such as neutrophils, monocytes, and natural killer cells, and in epithelial cells lining the respiratory tract and this has a major role in protecting the lung from infection.

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