.Who's missing out?
Studies among the general population in Australia have found that 23-49% of people suffer mild vitamin D deficiencies. Another 7-10% suffer from moderate to severe deficiencies.
This article explains:
What is vitamin D?
Vitamin D is primarily known for its role in bone health. It helps with the absorption of calcium and phosphate, reduces calcium loss from bones and is needed for bone growth and remodelling.
There are suggestions that it also plays an important role in other aspects of human health, especially immunity and infection control, and recent research on tuberculosis bacteria has shed light on the critical role vitamin D plays in the function of T-cells, which are white blood cells that fight infection in the body.
It’s also linked with fighting flu and other respiratory infections due to its role in the production of infection-fighting amino acids (antimicrobial peptides).
Our main source of vitamin D comes from exposure to sunlight. A steroid in the skin, called 7-dehydrocholesterol (7-DHC), is converted to vitamin D3 – called cholecalciferol – through the action of solar UVB radiation.
Other minor sources of vitamin D3 are fatty fish, eggs, meat and fortified foods. Vitamin D2 (ergocalciferol) comes from fungi, and may be used in supplements.
Some people are at higher risk of deficiency including:
- People who are housebound, or living in a long-term care facility, such as a nursing home, or shift workers who sleep through the day. Studies have found that up to 77% of aged care residents are deficient.
- People with naturally dark skin Dark skin has a sun protection factor of up to 15 – so, the equivalent of wearing SPF15 sunscreen. In equatorial regions, where there’s plenty of sun, this isn’t such a problem, but dark-skinned people living further north or south may need supplements.
- People who cover themselves for religious or cultural reasons, or due to increased risk of skin cancer or other skin conditions.
- People who live in southern parts of Australia have a higher risk of deficiency than those in the north, although people in the north may also be at risk due to skin cancer prevention measures.
- Obese people Vitamin D is readily taken up by fat cells, and it’s believed obese people have vitamin D stored in body fat instead of doing what it should do elsewhere in the body.
- Elderly people have lower concentrations of the 7-DHC in the skin, and need larger amounts of sun than younger people. To avoid skin damage, though, supplements are a safer option.
- People with certain diseases or conditions suffer from reduced vitamin D absorption and/or synthesis, including Crohn’s disease, coeliac disease, inflammatory bowel disease, cystic fibrosis, chronic pancreatitis, and kidney or liver disease.
- Certain medications also contribute to vitamin D deficiency, including rifampicin (an antibiotic) and anticonvulsants.
The most common results of vitamin D deficiency are:
- Rickets (softening of the bones during childhood)
- Osteomalacia (softening of the bones in adults which causes pain in the bones, and often joints and muscles)
- Osteoporosis (porous bones)
These issues in turn can lead to bone fractures, which can mean the end of independent living for the elderly.
Vitamin D deficiency is also blamed for many other health effects not related to our bones. People living further from the equator, where there are lower UV radiation levels, are at increased risk of:
- Multiple sclerosis
- Type 1 diabetes
- High blood pressure
All of these conditions have been linked with vitamin D levels in at least one study.
Low levels of vitamin D have also been associated with increased risk of developing colorectal, breast, prostate and other cancers, as well as the metabolic syndrome.
Conversely, giving vitamin D supplements to people at risk of deficiency has been found to reduce the risk of multiple sclerosis and certain cancers, and prevent falls in the elderly.
But it’s important to note that many of these findings are based on preliminary research, and some authorities have questioned the benefits of vitamin D for reasons other than bone health and falls prevention. A review by the National Prescribing Service points out that many of the studies are observational, have design limitations or are contradictory.
A recent review of over 1000 studies by the US Institute of Medicine reported a general lack of evidence for a causal relationship between vitamin D deficiency and many of the associated disorders mentioned above – that is, it can’t be proven that vitamin D deficiency actually caused the problem. They were also critical of claims for benefits from taking unnecessary supplements, describing them as ‘overblown’, concluding there were no health guarantees other than for healthy bones (when taken with calcium).
Vitamin D deficiency is largely symptomless, and may not be suspected unless the individual suffers an unusual fracture, or has one or more risk factors. Deficiency can be determined by measuring the levels of 25-OHD, the main form of circulating vitamin D. The degree of deficiency is determined according to the 25-OHD levels in the blood.
- Vitamin D sufficiency >75 nmol/L
- Sub-optimal Vitamin D 50-75 nmol/L
- Mild deficiency 25-50 nmol/L
- Moderate deficiency 15-25 nmol/L
- Severe deficiency <15 nmol/L