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Very high blood levels of vitamin D confer no additional benefit, researchers from Johns Hopkins reported in the American Journal of Medicine. In fact, when they combined the results of their present and previous studies, they found that raising vitamin D levels in “healthy people” with already normal levels may be potentially harmful.
Healthy people and health care professionals have been bombarded with stories from health websites and the media about the hazards of low vitamin D levels, urging people to take supplements to protect against hardening of the arteries,hypertension, diabetes, weak bones, and a range of other illnesses.
Study leader Muhammad Amer, M.D., M.H.S., said:
“Healthy people have been popping these pills, but they should not continue takingvitamin D supplements unchecked. At a certain point, more vitamin D no longer confers any survival benefit, so taking these expensive supplements is at best a waste of money.”
Some people definitely do benefit from higher vitamin D blood levels and should be considered for supplements, they include:
- elderly women
- patients with kidney disease
- postmenopausal women
- very obese people
In this study, Dr. Amer and Dr. Rehan Qayyum reviewed data from over 10,000 participants in NHANES (National Health and Nutrition Examination Survey) from 2001 to 2004. They then matched the data they had gathered with those contained in the National Death Index through the end of 2006.
When they examined details on deaths from all causes and specifically cardiovascular disease, they found that people whose blood levels were at the top range of what the Institute of Medicine considers “adequate” (21 nanograms per milliliter of 25-Hydroxyvitamin D) had a 50% lower risk of dying prematurely.
However, as blood levels of vitamin D rose above 21 nanograms per milliliters, that protective effective seemed to wear off.
The main source of vitamin D is skin exposure to direct sunlight. Vitamin D can be found naturally in a small number of foods, including salmon, sardines and mackerel (oily fish). Commercially sold milk, fat spreads and some breakfast cereals are fortified with vitamin D.
Many people are starting to wonder whether they should be slapping on so much sunscreen when going outdoors if sunlight is the main source of vitamin D, Dr. Amer explained. The problem is, no set amount of supplementation can raise vitamin D levels to 21 nanograms per milliliter because we do not all process vitamins in the same way.
Amer and Qayyum found that if blood vitamin D levels are increased, the result is lower levels of CRP (c-reactive protein), a popular marker for cardiovascular inflammation.
However, excessive vitamin D levels may be bad for you – any vitamin D levels above 21 nanograms per milliliter were found to be linked to an increase in CRP, which is associated with the hardening of blood vessels and a greater risk of developing cardiovascular problems.
The team has also found a link between excess vitamin D and raised levels of homocysteine, which can increase the risk of cardiovascular diseases.
Dr. Amer urges people to check with their doctors before considering vitamin D supplements – ideally, they should have their vitamin D blood levels checked.
Even if your doctor recommends supplementation for you, you should beware when reading the labels. A report published in JAMA Internal Medicine found that many OTC vitamin D supplements have less of the vitamin than their labels claim (OTC means “over-the-counter”, non-prescription).
“Most healthy people are unlikely to find that supplementation prevents cardiovascular diseases or extends their lives,” and there is no consensus among doctors on what is the right level of vitamin D in the blood for healthy people.
There are a lot of myths out there and not enough data.”
This study is supported by a grant from the National Heart Lung and Blood Institute (1K23HL105897-01).
Boston team finds many benefits from higher vitamin D levels
A team from Boston University School of Medicine reported in the journal PLoS ONE (March 2013 issue) that higher vitamin D levels in healthy people have an impact on genes involved in many biologic pathways associated with cardiovascular, autoimmune and infectious diseases, as well as cancer.
The authors say that healthy people who improve their vitamin D status have considerably better immunity against disease.
In another study carried out at Dextrel University, also published in PLoS ONE (February 2013 issue), scientists found a link between obesity and vitamin D deficiency – they found thatobesity can cause vitamin D deficiency. The study involved 42,000 people in more than 21 countries.