The latest in a series of studies revealing unexpected benefits from vitamin D has shown that a calcium- and vitamin D-rich diet may reduce the risk of premenstrual syndrome.
Researchers queried about 3,000 women from 1991 to 1999 as part of the Harvard Nurses' Health Study to determine how much calcium and vitamin D women ingested through their diet and supplements. Researchers did not measure how much vitamin D participants got from sunlight.
None of the women in the study had experienced PMS when the study began. The authors tracked how many of the women developed PMS, and found that women who consumed high amounts of vitamin D through food or supplements had a 40 percent lower chance of developing PMS than those with lower vitamin D intake.
PMS affects women before their menstrual period begins with several symptoms, including depression, irritability, abdominal cramping and headaches. Dr. Chandra Graham, an assistant professor of obstetrics at the University of Maryland School of Medicine, said 40 to 50 percent of women experience symptoms, but only 10 to 15 percent have severe PMS.
Vitamin D and calcium are closely related in most diets because both are available in fortified milk.
Less PMS with RDA
The women who consumed the recommended daily allowances of calcium and vitamin D experienced the lowest risk of PMS, said Elizabeth Bertone-Johnson, one of the study's authors and an epidemiologist at the University of Massachusetts. Most women can meet these requirements with four daily servings of milk fortified with vitamin D.
The more milk women drank, the lower their chances of developing PMS, the study showed. Women with the highest risk of developing PMS consumed only one serving or less of milk a week, she said. Nationwide, many women are likely to miss out on either nutrient or both, she added.
"There are pretty good data suggesting a relatively large percentage of the population aren't meeting the RDA for calcium," she said.
Graham estimates that more than half of women nationwide do not meet the RDA for calcium. "People may believe they're getting enough calcium from their diet, but they're actually not," she said.
Often, multivitamins only contain half of the RDA for calcium, and some women think one 8-ounce glass of milk a day is enough, she said. The study did not conclusively prove whether calcium supplements were as effective as calcium from the diet.
Since this is the first study of its kind, it is difficult to conclude whether women should be taking more calcium or vitamin D, Bertone-Johnson said. Although an overdose of calcium is proven to be harmful, she said she doesn't know whether too much vitamin D can have adverse effects.
Added Graham: "Making sure you meet the RDA would probably suffice."
Researchers found that only reduced-fat milk effectively lowered the risk of developing PMS, but Bertone-Johnson said it wasn't clear whether the fat in whole milk was responsible for its lack of effect on PMS.
A recent Japanese study found a relationship between saturated fat and severity of PMS symptoms, and the nurses' study itself found that overweight women were more likely to develop PMS in the first place--although Bertone-Johnson said she doesn't know why.
There are several possible reasons for vitamin D's apparent effect on PMS onset, she said. One is the vitamin's little-understood relationship with estrogen, its role in regulating calcium absorption and its potential effects on brain tissue, which may counteract the symptoms of depression during PMS.
Scientists are just beginning to discover a wide range of potential benefits from the vitamin, and this study is likely to add to that store of knowledge.
Recent reports show that vitamin D may help prevent and treat several types of cancer, including lymphoma, colon cancer and prostate, lung and skin cancers.
One Harvard researcher has even suggested that vitamin D produced by regular exposure to sunlight prevents 30 deaths for every one caused by skin cancer.
This seemingly good news has sparked a fiery debate in scientific circles, since the best source of vitamin D is sunshine. Researchers who urge consumers to leave their sunblock at home a couple of times per week to increase the body's vitamin D production have infuriated skin-cancer specialists who spent decades convincing patients to keep out of the sun.
Some scientists doubt how much vitamin D we can actually extract from our diets, and Bertone-Johnson said her study doesn't necessarily establish a link between diet and vitamin D levels in the body.
"Our findings are interesting and provocative, and might add more information to the discussion," she said.
The researchers would like to study specifically whether exposure to sunlight would likewise lower the risk of developing PMS.
Dr. Barbara Gilchrest, professor and chairman of the dermatology department at Boston University's medical school, agreed that more research needs to be done before scientists can reach conclusions about vitamin D and PMS.
"Given that probably most people get most of their vitamin D from sun exposure, this is a huge omission," she said. "It certainly says nothing about whether you need to go out into the sun."