Vitamin D has many health benefits, and new information about its role in the prevention of diseases such as cancer keeps emerging. Current debate revolves around recommended daily intakes. Recommended levels tend to be much higher outside the Nordic countries.
vitamin d In the summer, Finns who eat a typical diet obtain most of their vitamin D from sun exposure. Elderly people are an exception to this rule because they tend to spend more time indoors, and even if exposed to sunlight, their skin produces only a third of the amount of vitamin D produced by younger skin. Many Finns do not get enough vitamin D in winter.
Effects
emerge slowly
“The wide-ranging effects of vitamin D at the cellular level make population-based studies an attractive prospect. These studies could reveal vitamin D’s connection to various illnesses,” says Ilari Paakkari, Professor of Pharmacology at the University of Helsinki, in an article in the TABU journal published by the Fimea, Finnish Medicines Agency.
According to Professor Paakkari, studies carried out in mice indicate that a low level of vitamin D intake increases the risk of developing various illnesses.
Serious vitamin D deficiency causes rickets in children, but the possible effects of low intake on circulatory diseases, cancer and the immune system are revealed slowly over the decades. This is why proof of the preventive effects of vitamin D has so far been mostly related to the frequency of various illnesses.
In experimental research, which studies the health benefits of vitamin D, the doses have often been low, approximately 10 micrograms (µg). Even so, the results indicate that vitamin D taken with calcium can reduce the risk of bone fractures.
Deficiency
causes problems
According to Professor Paakkari, the proof of the connection between low vitamin D levels and many illnesses and defects is strong enough to warrant experimental research, which can give us more information on the frequency of illnesses.
According to current research, vitamin D deficiency is linked to osteoporosis and there are indications that it is also connected to falls in old age (muscular weakness), the development of certain cancers, the body’s ability to prevent infections, gingivitis and high blood pressure. Current studies focus on the connection between vitamin D and diabetes, autoimmune diseases, multiple sclerosis and osteoarthritis.
A hormone that
maintains health
Vitamin D turns to calcidiol in the liver. Blood calcidiol concentration is the best indicator of vitamin D levels in the body. Our bodies turn calcidiol into calsitriol, which is a hormone. It affects several functions in the body, including calcium absorption in the intestine.
The view of vitamin D as a hormone that maintains overall health of the body has strengthened further over the recent years. Today, there is a lot of information available about the health benefits of the vitamin, and researchers are debating over the optimum recommendation levels of vitamin D that would best yield these benefits.
Toxic
in large doses
In excess, vitamin D is toxic. In Finland, the recommended maximum daily intake for adults is 50 µg. The recommended safe daily intake level for children is 25 µg. In practice, harmful overdoses are extremely rare.
Young children may develop symptoms of vitamin D poisoning if their long-term intake exceeds the recommended levels by 2.5 to 5 times. Adults require very large quantities (approx. 1,200 µg/day) before developing any symptoms.
Large quantities of vitamin D increase the absorption of calcium and phosphate in the alimentary canal and their bone resorption and also reduce the secretion of calcium through the kidneys. An overdose may cause deposits of calcium salts in soft tissues.
Symptoms of vitamin D poisoning include lack of appetite, thirst, nausea, alimentary symptoms and headache. Serious hypercalcaemia, i.e. an elevated level of calcium in the blood, requires hospital treatment.
Current recommendations
too low
According to the current recommendation given by the National Nutrition Council, the daily intake of vitamin D for over 3-year-olds and adults should be at least 7.5 µg and for under 3-year-olds and over 60-year-olds at least 10 µg.
New recommendations are currently being drafted. According to Professor Christel Lamberg-Allardt, who chairs the vitamin D committee, new Finnish recommendations will be based on the Nordic nutrition recommendations, which will come into effect in 2012.
Increasing the recommended levels is supported by numerous studies, such as those focusing on bone mineral density and risk of fractions. The Finnish Osteoporosis Society is among those in favour of increasing the recommended levels.
”Elderly adults benefit from a daily intake of 20 micrograms to prevent fractures. This is a widely shared view among scientists today,” says Professor Lamberg-Allardt. Professor Paakkari agrees.
Problem for countries
with less sunlight
Many countries recommend much higher daily intake levels than Finland. These recommendations are based on recent studies.
The expert group of the U.S. Food and Drug Administration for example recommends that over 4-year-olds obtain 25 µg of vitamin D daily. The Canadian Cancer Society, which operates in a Northern country with little sunlight similar to Finland, makes the same recommendation. For over 50-year-olds, the recommendation stands throughout the year.
Medical literature has suggested even higher recommendations for adults in countries with less sunlight, even as high as 100 µg.
Maximising the benefits
and minimising the adverse effects
Based on research results, Professor Paakkari considers calcidiol concentration of 80–100 nmol/l an optimal level which maximises the benefits and minimises the adverse effects of vitamin D. This equals about 100 µg of vitamin D daily from food, sunlight and supplements. Even though this level is higher than the reference value used by many Finnish laboratories (40–80 nmol/l), it is a natural level which the skin can produce in the Southern sun.
“Reliable research results indicate that these concentration levels together with calcium intake reduce the risk of osteoporosis among the aged population. A concentration of approximately 80 nmol/l prevents the secretion of parathyrin, a hormone which maximises bone resorption, in young adults. Elderly adults require a larger concentration of 100 nmol/l.”
Vitamin D levels should be
measured more often
According to Professor Paakkari, the levels of calcidiol in the blood of Finns should be measured more often. If we did, we could start the prevention of osteoporosis early enough by vitamin D prescriptions.
Christel Lamberg-Allardt wants to wait for further results from more extensive studies in which larger doses of vitamin D have been tested. She also points out that many studies indicate that a daily intake of 20 to 25 µg can raise the blood serum calcidiol concentration in winter to 80 nmol/l.
“We already have a good theoretical foundation, but we still have some way to go before we can surely know what kind of vitamin D intake levels can help prevent illnesses and what are the real adverse effects,” she emphasises.
Text Pertti Suvanto | Photo Istockphoto