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Two new studies find problems when vitamin D levels are low. From Science Daily:

Low vitamin D levels linked to increased risks after noncardiac surgery

Patients with low blood levels of vitamin D are at increased risk of death and serious complications after noncardiac surgery, suggests a study. The researchers analyzed the relationship between vitamin D level and surgical outcomes in approximately 3,500 patients who underwent operations other than heart surgery between 2005 and 2011. Only patients who had available data on vitamin D levels around the time of surgery -- from three months before to one month afterward -- were included in the study.

Most patients did not meet the recommended 25-hydroxyvitamin D concentration of greater than 30 nanograms per milliliter (ng/mL). The median vitamin D level was 23.5 ng/mL -- more than 60 percent of patients were in the range of vitamin D insufficiency (10 to 30 ng/mL). Nearly 20 percent had vitamin D deficiency (less than 10 ng/mL).

"Higher vitamin D concentrations were associated with decreased odds of in-hospital mortality/morbidity," the researchers write. For each 5 ng/mL increase in 25-hydroxyvitamin D level, the combined risk of death, cardiovascular events, or serious infections decreased by seven percent.

From Science Daily:

Vitamin D deficiency may reduce pregnancy rate in women undergoing IVF

Women with a vitamin D deficiency were nearly half as likely to conceive through in vitro fertilization (IVF) as women who had sufficient levels of the vitamin, according to a new study. Long known for its role in bone health, vitamin D is a steroid hormone that is emerging as a factor in fertility.

Women who had sufficient levels of vitamin D were nearly twice as likely to conceive as their counterparts with vitamin D deficiency. Since women with sufficient levels of the hormone were more likely to produce top-quality embryos, researchers theorized vitamin D was involved in the production of quality eggs in the ovaries as well as the successful implantation of embryos in the uterus.

Another study finding risks from too low vitamin D levels. From Science Daily:

Lower vitamin D level in blood linked to higher premature death rate

Researchers at the University of California, San Diego School of Medicine have found that persons with lower blood levels of vitamin D were twice as likely to die prematurely as people with higher blood levels of vitamin D.

The finding, published in the June 12 issue of American Journal of Public Health, was based on a systematic review of 32 previous studies that included analyses of vitamin D, blood levels and human mortality rates. The specific variant of vitamin D assessed was 25-hydroxyvitamin D, the primary form found in blood.

This new finding is based on the association of low vitamin D with risk of premature death from all causes, not just bone diseases."

Garland said the blood level amount of vitamin D associated with about half of the death rate was 30 ng/ml. He noted that two-thirds of the U.S. population has an estimated blood vitamin D level below 30 ng/ml."This study should give the medical community and public substantial reassurance that vitamin D is safe when used in appropriate doses up to 4,000 International Units (IU) per day," said Heather Hofflich, DO, professor in the UC San Diego School of Medicine's Department of Medicine.

The average age when the blood was drawn in this study was 55 years; the average length of follow-up was nine years. The study included residents of 14 countries, including the United States, and data from 566,583 participants.

Two studies about Vitamin D. From Science Daily:

Vitamin D increases breast cancer patient survival, study shows

Breast cancer patients with high levels of vitamin D in their blood are twice as likely to survive the disease as women with low levels of this nutrient, report University of California, San Diego School of Medicine researchers in the March issue of Anticancer Research.

In previous studies, Cedric F. Garland, DrPH, professor in the Department of Family and Preventive Medicine, showed that low vitamin D levels were linked to a high risk of premenopausal breast cancer. That finding, he said, prompted him to question the relationship between 25-hydroxyvitamin D -- a metabolite produced by the body from the ingestion of vitamin D -- and breast cancer survival rates.

Garland and colleagues performed a statistical analysis of five studies of 25-hydroxyvitamin D obtained at the time of patient diagnosis and their follow-up for an average of nine years. Combined, the studies included 4,443 breast cancer patients.

Women in the high serum group had an average level of 30 nanograms per milliliter (ng/ml) of 25-hydroxyvitamin D in their blood. The low group averaged 17 ng/ml. The average level in patients with breast cancer in the United States is 17 ng/ml.

A 2011 meta-analysis by Garland and colleagues estimated that a serum level of 50 ng/ml is associated with 50 percent lower risk of breast cancer. While there are some variations in absorption, those who consume 4,000 International Units (IU) per day of vitamin D from food or a supplement normally would reach a serum level of 50 ng/ml. 

From Science Daily:

Vitamin D deficiency may compromise immune function

Older individuals who are vitamin D deficient also tend to have compromised immune function, according to new research accepted for publication in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM).

"Our data suggest vitamin D may be involved in maintaining the health of the immune system as well as the skeletal system," said one of the study's authors, Mary Ward, PhD, of the University of Ulster in Coleraine, U.K.

The observational study of 957 Irish adults who were at least 60 years old examined vitamin D levels as well as biomarkers of inflammation. Participants who were vitamin D deficient were more likely to have high levels of these biomarkers, which are linked to cardiovascular disease and inflammatory conditions such as multiple sclerosis and rheumatoid arthritis.