Doctor Doctor: Are ‘sunshine vitamin’ top-ups recommended in the winter?

Niahm Houston

Dear Doctor, Why is vitamin D so important to our health and how much does a person need to keep bones strong?

Why do we need vitamin D?

Vitamin D is needed for the absorption of calcium and phosphorous which is essential in maintaining healthy bones. It has also been shown to reduce the risk of rheumatoid arthritis in women and reduces the severity of asthma. It is an immune-system regulator and may be involved in reducing the risk of developing multiple sclerosis. It is also probably linked to maintaining a healthy weight. Studies have shown that people with adequate vitamin D seem to have less risk of developing cancer, compared to people with lower levels.

Why is it called the sunshine vitamin?

Vitamin D is made in your skin when you are exposed to sunlight. We need 10-15 minutes of sun exposure at least twice a week on unprotected skin to produce enough Vitamin D. But cloud cover, smog and wearing sunscreen all interfere with our body's production of this essential vitamin. At this time of the year in countries such as Ireland, our exposure to sunlight can be considerably less.

If you are at risk of deficiency you should take vitamin D supplements daily. But your body also needs other substances found in a well-balanced diet to absorb vitamin D. Sources of vitamin D include fatty fish (salmon, tuna, mackerel) egg yolks, cod liver oil and fortified foods (cereals, milk, spreads, other dairy products, flour). Cooking does not affect the amount of vitamin D in foods.

How much vitamin D do I need? How do you know if you do not have enough?

These are the recommended amounts for people who do not have enough exposure to sunlight.

  • Up to 50 years -- 5mcg or 200IU daily.
  • 50 to 70 years -- 10mcg or 400IU daily.
  • 71+ years 15mcg or 600IU daily.

A blood test measuring the level of "25-hydroxy vitamin D" is the most accurate way to measure how much is in your body. Normal range is between 30-74 ng/ml.

Can a lack of it lead to any illnesses?

Yes, osteomalacia (softening of the bone) caused by demineralisation can affect adults and cause severe musculoskeletal pain.

Osteoporosis, a condition common in many post-menopausal women causes increased bone fragility and increases your risk of a fractures.

Rickets affects children and their bones become distorted because they are soft.

Vitamin D deficiency has also been linked to heart disease, cancer, multiple sclerosis, chronic pain, immune-system problems such as inflammation and Alzheimer's disease.