Most doctors and scientists who are knowledgeable about vitamin D suggest at least 2000 IU (IU = International Units, 40 IU = 1 microgram) per day is a safe and appropriate dose, that is just one microtab per day from our 2000 IU bottle. However 2000 IUs is not enough to raise everyone’s vitamin D level to an optimum. Some people need to take 5000 IU per day (one of our 5,000 IU microtabs) and some even 10,000 IU (two 5,000 IU microtabs), because people vary in the way they break down and excrete vitamin D.
What is a safe dose? The US Institute of Medicine has identified 4000 IU per day as a safe dose (two of our 2,000 IU microtabs), but other studies have shown that many people are able to take an average of 10,000 IU per day for a year without any problems. A dose above 4,000 IUs per day (one of our 5,000 IU microtabs per day) is appropriate when taking vitamin D for the first time, for people over 60, for those who are overweight, in winter, and for people who have a disease such as diabetes, arthritis, or cancer which there is reason to believe may respond to vitamin D.
If you have not taken vitamin D before it makes sense to build up your blood level quickly by taking a generous “loading” dose. We suggest you do this by taking one of our 5,000 IU microtablets daily for three to six months. After that you may be able to manage with a lower “maintenance” dose of one 5000 IU tablet five times per week – i.e. weekdays only – or you can take two of our 2000 IU microtablets a day. Some people will be able to get enough from one 2,000 IU microtablet a day – you can try that and test yourself (see below) after a couple of months to see if you are getting enough.
If you wish you can take a weekly maintenance dose of five 5,000 tablets once a week. Weekly, or even monthly, dosing (pro rata) is possible because vitamin D is not at all toxic and builds up slowly in the body (it has a long half life). It is perfectly safe to take individual doses of 100,000 IUs of vitamin D monthly. But it is more natural, more physiological, to take a regular dose on a daily, or roughly daily, basis, just as if you were getting natural sun exposure most days.
How do I know if I am taking enough vitamin D? The majority of people will get enough vitamin D if they take an average of 4-5,000 IUs per day and need not worry about testing. However a test is reassuring. Most knowledgeable doctors agree that a blood level of vitamin D (measured as 25(OH)D) above 80 nmols/l (40 ng/ml) is desirable. To provide a margin that allows for seasonal changes it is probably best to aim for a level of 25(OH)D above 100nmols/l. Levels up to 200 nmols/l are not associated with any overt toxic symptoms.
I overdose by taking too much vitamin D? It is very difficult to take
too much vitamin D and there is no danger of overdosing if this advice
If you are able to sunbathe in summer (May to September) for at least half an hour three times a week between 11am and 3.00pm – substantially longer at other times of day – then you will not need to take a supplement in the summer. However in the UK our cloudy climate makes this difficult for most people to achieve and we recommend a summer dose of 2000 IUs per day as a summer supplement for keen but frustrated sunbathers. Winter sun (October to March) in Europe and the northern United States and Canada is too weak to provide any useful vitamin D and so it is wise to take a full supplement during these months.
If you suffer from a chronic disease such as arthritis, MS or cancer it is helpful to know that your vitamin D has reached the optimum level. Under these circumstances many GPs will agree to order a test but it is not easy for GPS in the UK because pathologists, the doctors who run the labs, are defending their budgets and are often reluctant to agree to tests. Some doctors believe that people with cancer, and some other diseases that may respond to vitamin D such as MS, should aim for a high normal blood level of vitamin D between 125 and 150 nmols/l (equivalent to between 50 to 60 ngs/ml), The reasoning behind this is that in illness some body tissues may be resistant to vitamin D and a high level may push more through the system.
What is vitamin D3 and is it better than vitamin D2? Vitamin
D3 is the natural human or animal form of vitamin D called
colcalciferol or cholecalciferol. It is extracted from UV irradiated
lanolin, the fat that occurs in sheep’s wool. Vitamin D2 or
ergocalciferol occurs in fungi and certain plants that have been in
sunshine. Vitamin D3 is about twice as potent as vitamin D2 and is
preferred by most people because it is the natural human molecule. Some
vegans prefer vitamin D2.
Cod liver oil is a natural source of vitamin D3 but modern cod liver oil has the vitamins extracted and added back. Most modern cod liver oils are made with a high ratio of vitamin A to vitamin D. This means that a high enough dose of vitamin D cannot be obtained without taking an excessive dose of vitamin A. The large amount of vitamin A also interferes with the normal action of vitamin D and so cod liver oil is not recommended.
it safe to take vitamin D in pregnancy and when breast feeding? Yes it
is. The UK government recommends that pregnant women and nursing mothers
take 400 IUs of vitamin D per day but until recently few women were
aware of this. However this dose is considered to be very low by certain
medical authorities. A dose ten times larger, 4,000 IUs per day, has
been shown by two US pioneers, Drs Hollis and Wagner at the Medical
University of South Carolina, to be completely safe in pregnancy and to
What dose is recommended for babies? In most countries it is recommended that babies are started on 200 to 400 IUs of vitamin D from the first week of life. This is particularly important for breast fed babies because breast milk of modern women generally contains very little vitamin D. Artificial milk formula is supplemented with vitamin D and so it is not so important to give a vitamin D supplement to babies on formula, although even these babies may be deficient in vitamin D if their mothers are seriously deficient. It is generally safe to give an additional 200-400 IU daily supplement to a bottle fed baby. All babies should be given a supplement from weaning onwards because normal food does not contain enough vitamin D and babies today are often over-protected from sunlight.
What dose of vitamin D should I give to my older children? By the age of one year babies are ready for a larger dose of vitamin D and can safely be given 1000 IUs per day. From school age (four to five years) to puberty 2000 IUs per day is a safe and suitable dose. From puberty on an adult dose of about 3,000 IUs a day is probably optimal.
Will I and my children have to take vitamin D for the rest of our lives? Yes it is advisable. You may at first think that this is not natural, but we need to take extra vitamin D for optimal health because of the artificial lives we lead today. The first human pioneers that came to Britain lived outdoors and ate a diet rich in fish which provides a lot of vitamin D. They evolved white skins which makes vitamin D several times faster than white skin. Even when agriculture began they spent most of their time outdoors. But in the last two hundred years industrialisation has brought us to live indoors – and in the last 20 years we spend even more time indoors in front of screens. Our lives today are artificial but by taking vitamin D we do something to make our lives a bit more natural.