Although African-Americans have a higher rate of vitamin D deficiency as well as a greater incidence of strokes, compared to other racial groups in the USA, vitamin D deficiency increases the risk of death from stroke for whites but not for blacks, researchers from Hopkins University School of Medicine in Baltimore will explain on Monday at the American Heart Association’s Scientific Sessions 2010, Chicago.

A Caucasian person with vitamin D deficiency runs twice the risk of dying from a stroke compared to a white person with adequate levels of vitamin D, the researchers revealed after gathering data from files involving 7,891 black and white adults in the USA.

The investigators were surprised to find no link between deadly strokes and lack of vitamin D among African-Americans, even though the overall dying-from-stroke risk among blacks is about 60% higher compared to whites.

Even after taking account of certain factors which could have an impact on their findings, the researchers found that the results still held true. 32% of blacks were found to lack vitamin D, versus almost 7% of whites.

Erin Michos, M.D., M.H.S., said:

    “We thought maybe the lower vitamin D levels might actually explain why blacks have higher risks for stroke. But we did not find the same relationship between vitamin D and stroke in blacks.”

Study after study appears to be revealing an ever wider range of vitamin D benefits, including protection from rickets, severe bone loss, heart disease, cancer, diabetes, multiple sclerosis, and other diseases and conditions.

Vitamin D is a fat-soluble steroid vitamin which encourages calcium and phosphorous absorption and metabolism. Individuals who get normal quantities of sunlight exposure do not require additional vitamin D supplements. Sunlight promotes adequate quantities of vitamin D synthesis in the skin. Scientists know about five forms of vitamin D – D1, D2, D3, D4, D5. Vitamins D2 (ergocalciferol) and D3 (cholecalciferol) seem to matter the most to humans.

Apart from sunlight, other sources of vitamin D include fatty fish, fortified milk products and breakfast cereals, and egg yolks.

The investigators gathered information from NHANES-III (Third National Health and Nutrition Examination Survey of Americans) which was carried out between 1988 and 1994. The participants were followed-up for an average of 14 years. Information on blood levels of 25-hydroxyvitamin D was collected on each individual – this can show a person’s vitamin D levels stored in the body.

They found that African-Americans had considerably lower levels of vitamin D compared to Caucasians. According to the National Death Index, there were 166 fatalities from stroke among whites, and 60 among blacks.

They tried to link low vitamin D levels to fatal strokes according to race, after ruling out such factors as socioeconomic status, diabetes, hypertension, cholesterol levels, BMI (body mass index), smoking status, alcohol consumption and physical activity.

Michos and team believe blacks are naturally resistant to the negative consequences of vitamin D deficiency. She added that they also found a lower incidence of bone fractures among black with low vitamin D levels, compared to whites with the same deficiency.

Michos said:

    “Since stroke is the No. 3 cause of death in the United States, it’s important for us to consider low vitamin D as a possible risk factor for stroke at least among whites.”

The researchers say further trials are needed to find out whether vitamin D deficiency treatment might help reduce stroke risk.

This study only looked at deaths from stroke, it did not assess or attempt to link vitamin D levels with outcomes for survivors of stroke. Also, vitamin D levels were only measured at the beginning of the study, so they might not have fully reflected every individual’s overall long-term vitamin levels.

Source: American Heart Association’s Scientific Sessions 2010

Written by Christian Nordqvist