The vitamin D levels of newborn babies appear to predict their risk of respiratory infections during infancy and the occurrence of wheezing during early childhood, but not the risk of developing asthma. Results of a study in the January 2011 issue of Pediatrics support the theory that widespread vitamin D deficiency contributes to risk of infections.
“Our data suggest that the association between vitamin D and wheezing, which can be a symptom of many respiratory diseases and not just asthma, is largely due to respiratory infections,” says Carlos Camargo, MD, DrPH, of the Massachusetts General Hospital (MGH), who led the study. “Acute respiratory infections are a major health problem in children. For example, bronchiolitis – a viral illness that affects small airway passages in the lungs – is the leading cause of hospitalization in U.S. infants.”
Although vitamin D is commonly associated with its role in developing and maintaining strong bones, recent evidence suggests that it is also critical to the immune system. Vitamin D is produced by the body in response to sunlight, and achieving adequate levels in winter can be challenging, especially in regions with significant seasonal variation in sunlight. Previous studies by Camargo's team found that children of women who took vitamin D supplements during pregnancy were less likely to develop wheezing during childhood. The current study was designed to examine the relationship between the actual blood levels of vitamin D of newborns and the risk of respiratory infection, wheezing and asthma.
The researchers analyzed data from the New Zealand Asthma and Allergy Cohort Study, which followed more than 1,000 children in the cities of Wellington and Christchurch. Midwives or study nurses gathered a range of measures, including samples of umbilical cord blood, from newborns whose mothers enrolled them in the study. The mothers subsequently answered questionnaires – which among other items asked about respiratory and other infectious diseases, the incidence of wheezing, and any diagnosis of asthma – 3 and 15 months later and then annually until the children were 5 years old. The cord blood samples were analyzed for levels of 25-hydroxyvitamin D (25OHD) – considered to be the best measure of vitamin D status.
Cord blood samples were available from 922 newborns in the study cohort, and more than 20 percent of them had 25OHD levels less than 25 nmol/L, which is considered very low. The average level of 44 nmol/L would still be considered deficient – some believe that the target level for most individuals should be as high as 100 nmol/L – and lower levels were more common among children born in winter, of lower socioeconomic status and with familial histories of asthma and smoking. By the age of 3 month, infants with 25OHD levels below 25 nmol/L were twice as like to have developed respiratory infections as those with levels of 75 nmol/L or higher.
Survey results covering the first five years of the participants' lives showed that, the lower the neonatal 25OHD level, the higher the cumulative risk of wheezing during that period. But no significant association was seen between 25OHD levels and a physician diagnosis of asthma at age 5 years. Some previous studies had suggested that particularly high levels of vitamin D might increase the risk for allergies, but no such association was seen among study participants with the highest 25OHD levels. Camargo notes that very few children in this study took supplements; their vitamin D status was determined primarily by exposure to sunlight.
An associate professor of Medicine at Harvard Medical School, Camargo notes that the study results do not mean that vitamin D levels are unimportant for people with asthma. “There's a likely difference here between what causes asthma and what causes existing asthma to get worse. Since respiratory infections are the most common cause of asthma exacerbations, vitamin D supplements may help to prevent those events, particularly during the fall and winter when vitamin D levels decline and exacerbations are more common. That idea needs to be tested in a randomized clinical trial, which we hope to do next year.”
Co-authors of the Pediatrics paper are Ravi Thadhani, MD, and Janice Espinola, MPH, from MGH; Tristram Ingham, MBChB, Kristin Wickens, PhD, and Julian Crane, FRACP, from University of Otaga, Wellington, New Zealand; Karen Silvers, PhD, Michael Epton, PhD, FRACP, and Philip Pattemore, MD, FRACP, from University of Otago, Christchurch, NZ; and Ian Town, DM, from University of Canterbury, Christchurch, NZ. The study was supported by grants from the Health Research Council of New Zealand, the David and Cassie Anderson Bequest and the MGH Center for D-receptor Activation Research.
“However,” the researcher said, “there is a lack of clinical studies of the effect of vitamin D supplementation for preventing respiratory infections.”
For the current study, Laaksi's team randomly assigned 164 male military recruits to take either 400 international units (IU) of vitamin D or inactive placebo pills every day for six months — from October to March, covering the months when people's vitamin D stores typically decline and when respiratory infections typically peak.
At the end of the study, the researchers found no clear difference between the two groups in the average number of days missed from duty due to a respiratory infection — which included bronchitis, sinus infections, pneumonia, ear infections and sore throat.
On average, men who took vitamin D missed about two days from duty because of a respiratory infection, compared with three days in the placebo group. That difference was not significant in statistical terms.
However, men in the vitamin D group were more likely to have no days missed from work due to a respiratory illness.
Overall, 51 percent remained “healthy” throughout the six-month study, versus 36 percent of the placebo group, the researchers report.
The findings, Laaksi said, offer “some evidence” of a benefit from vitamin D against respiratory infections.
Still, the extent of the benefit was not clear. While recruits in the vitamin group were more likely to have no days missed from duty, they were no less likely to report having cold-like symptoms at some point during the study period.
Moreover, recent studies on the usefulness of vitamin D for warding off respiratory ills have come to conflicting conclusions.
A study of Japanese schoolchildren published earlier this year found that those given 1,200 IU of vitamin D each day during cold and flu season were less likely to contract influenza A. Of 167 children given the supplement, 18 developed the flu, compared with 31 of 167 children given placebo pills.
On the other hand, a recent study of 162 adults found that those who took 2,000 IU of vitamin D everyday for 12 weeks were no less likely to develop respiratory infections than those given placebo pills.
Laaksi said that larger clinical trials looking at different doses of vitamin D are still needed before the vitamin can be recommended for curbing the risk of respiratory infections.
In the U.S., health officials recommend that adults up to the age of 50 get 200 IU of vitamin D each day, while older adults should get 400 to 600 IU. The upper limit is currently set at 2,000 IU per day; higher intakes may raise the risks of side effects.
Symptoms of vitamin D toxicity are often vague and include nausea, vomiting, constipation, poor appetite and weight loss. Excessive vitamin D in the blood can also raise blood pressure or trigger heart rhythm abnormalities.
Some researchers believe that people need more vitamin D than is currently recommended, and that intakes above 2,000 IU per day are safe. However, exactly what the optimal vitamin D intake might be remains under debate.
Food sources of vitamin D include milk, breakfast cereals and orange juice fortified with vitamin D, as well as some fatty fish, like salmon and mackerel. Experts generally recommend vitamin pills for people who do not get enough of the vitamin from food.
SOURCE: Journal of Infectious Diseases
The randomized, double-blind, placebo-controlled study, which was funded by The Dannon Company, Inc., involved 638 healthy children aged three to six, all of whom attended school five days a week. Parents were asked to give their child a strawberry yogurt-like drink every day. Some of the drinks contained the probiotic strain Lactobacillus casei (L. casei) and the others did not. Parents were also asked to record how many yogurt drinks their child consumed and to keep notes on their child's health.
At the end of the study, there was a 19 percent decrease in the number of common infections—e.g., ear infections, flu, diarrhea, sinusitis–among children who had consumed the yogurt drink with the probiotics than those who had the drink without the beneficial bacteria. When the researchers broke out the individual types of illness, they found that children who had the probiotic beverage had 24 percent fewer gastrointestinal infections (e.g., diarrhea, nausea, vomiting), and 18 percent fewer upper respiratory tract infections (e.g., ear, sinusitis, strep).
The reduction in infections did not, however, result in fewer days lost from school. Merenstein commented that “It is my hope that safe and tolerable ways to reduce illnesses could eventually result in fewer missed school days which means fewer work days missed by parents.”
The finding that the probiotic yogurt drink reduced infections in children, however, is significant. This joins results from other studies demonstrating benefits of probiotics in children, including one published in Pediatrics in which they reduced cold and flu symptoms, another in which they eased diarrhea, and one showing they helped prevent eczema in infants. Generally, probiotics have also been shown to benefit people who have celiac disease, irritable bowel, colitis, and possibly autism.
Georgetown University Medical Center