Are You Taking Vitamin D Supplement?

Perhaps you should.

Medical experts recommend that people at risk of Vitamin D deficiency take supplements daily.

The at-risk groups include older adults, people with little exposure to sunlight, dark-skinned people, and those on a vegan diet.

Why do Older Adults Need Vitamin D Supplement?

Vitamin D is available in two natural sources: (1) it is produced by the skin after exposure to ultraviolet B (UVB), and (2) it is present in a few types of food – oily fish, egg yolk, liver, cheese, and yoghurt.

Older adults are vulnerable to Vitamin D deficiency because:

  1. The skin is less efficient in producing Vitamin D as we grow older.
  2. The exposure to sunlight is inadequate.
  • Some elderly, especially those in care homes, spend little time outdoors due to mobility problems. Because UVB cannot pass through the glass, sitting near the window won’t help.
  • UVB radiation is affected by seasonal variation, latitude, and the time of day. People living in northern latitudes such as Ireland or Finland do not get much UVB in winter. While we are more likely to exercise outdoors in the morning or evening, UVB radiation is strongest around midday.
  1. They may not get sufficient Vitamin D from their diet because only a few types of food contain Vitamin D. It is particularly problematic for a vegan. A possible solution is taking Vitamin D fortified dairy, orange juices and cereals.
  2. The elderly may have problems with malabsorption, especially those with chronic liver diseases, Crohn’s Disease, and cystic fibrosis.
  3. Because melanin blocks the absorption of UV radiation, dark-skinned people are very vulnerable to Vitamin D deficiency if they are also subject to one or more of the above factors.

The Irish Longitudinal Study on Ageing (TILDA) at Trinity College Dublin found that 1 in 8 older adults in Ireland suffers Vitamin D deficiency4. And in winter, the rate goes up to 1 in 4. Even in summer, when the body normally produces Vitamin D, 5% of adults were deficient.

The researchers also found that Vitamin D deficiency increased with age. For example, of people over 80, 37% were deficient in winter, compared with 22% of aged 50-59 years. Those who were physically inactive were also much more likely to be deficient.

Lifestyle seems to play a part too. The study also found that Vitamin D deficiency was more common in smokers (23%), people who live alone (21%) and those from a lower socio-economic background (17%).

We may assume these findings are relevant to all countries with seasonal variations in sunlight.

What are the known problems of Vitamin D deficiency?

The liver converts vitamin D produced by the skin or absorbed from food to calcifediol, also known as 25(OH)D. Vitamin D deficiency is diagnosed if a person’s blood level of 25(OH)D is less than 12 mcg /ml (equivalent to 30 nmol/L).

Vitamin D is essential for maintaining normal blood levels of calcium and

Calcium with Vitamin D
Calcium with Vitamin D

phosphate. Therefore, Vitamin D deficiency leads to low bone density, resulting in osteopenia and osteoporosis. Abnormal calcium level also affects muscle contraction, nerve conduction, and the general cellular function of all body cells.

Vitamin D deficiency is known to be associated with muscle weakness. This problem is common among the elderly who are housebound. Muscle weakness is manifested by a feeling of heaviness in the legs, tiring easily, and difficulty climbing stairs and rising from a chair6.

Recent studies also link Vitamin D deficiency with heart disease, kidney disease, brain health, diabetes, immunity problems, Alzheimer’s disease and cancer. However, the results from these studies are still inconclusive, so further investigation is required.

Once these associations are confirmed, we could implement appropriate health policies to deal with high incidences of Vitamin D deficiency in the older adult population. Vitamin D deficiency can be treated easily with supplementation and food fortification.

What is the recommended dosage of Vitamin D?

Because there are still a lot of unknown factors surrounding Vitamin D and its effects on body tissues, medical experts have not agreed on the optimal level of Vitamin D for health benefits. The decision is also made difficult by regional, seasonal, lifestyle, genetic, and diet differences.

Suggestions from leading authorities are:

  • The US Institute of Medicine recommends 800 IU/day for adults above 70 years.
  • The American Geriatrics Society (AGS) recommends older adults take 1000 IU/day to help prevent fractures.
  • Public Health England (PHE) advises adults and children over one to take a daily supplement containing 10mcg* of Vitamin D, particularly during autumn and winter.
Multivitamin containing Vitamin D
Multivitamins containing Vitamin D

Most doctors think a daily dose of 800-1000 IU of Vitamin D will benefit the general health of ageing adults. This dosage is unlikely to cause harm unless there is another medical reason against it. You should consult your doctor or pharmacist if you have any doubts.

If you are taking multivitamins or calcium supplements, please check whether Vitamin D is already included in the supplement and how much. Again, it is prudent to check with your pharmacist if you are unsure.

Doctors can prescribe higher dosages to treat people with very low Vitamin D levels, especially if they are at high risk of falls. Of course, that has to be monitored carefully and reduced as soon as the high dosage is not required.

Excessive Vitamin D intake may cause Vitamin D Toxicity, which is harmful to health. For example, taking large doses of Vitamin D over a long period could weaken your bones.

Vitamin D has two forms: Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol). Most supplements contain D3. Studies suggest that D3 increases the blood level of 25(OH)D slightly better than D2.

Vitamin D2 and D3, whether produced naturally by the skin, absorbed from food, or taken as supplements, must be activated by the liver and kidneys before becoming useful. People with liver or kidney disease may need a special type of supplement from their doctors.




*Vitamin D in supplements is expressed in international units (IU) or micrograms (1µg).  One microgram (1µg) equals 40 IU of Vitamin D.



  1. National Institutes of Health Office of Dietary Supplements. Vitamin D – fact sheet for health professionals.
  1. Vitamin D Deficiency and Related Disorders.
  1. Kernisan, Leslie. Vitamin D: The Healthy Aging Dose (Plus Answers to 7 FAQs).
  1. One in eight older adults in Ireland is deficient in vitamin D.
  1. Getting Enough Vitamin D in Later Life.
  1. Janssen, H., Samson, M., Verhaar, H. Vitamin D deficiency, muscle function, and falls in elderly people. The American Journal of Clinical Nutrition, Volume 75, Issue 4, 1 April 2002, Pages 611–615.
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