14 April 2011

What African Americans should know about vitamin D and heart health

A while back, I was talking with a friend of mine. He was a giant of a black man and we spoke about his  blood pressure woes and his weight issues. So I asked him about his diet, his habits, and all that. He told me all about it: How he ate all the right foods, how he was trying to avoid the wrong ones, and how he recently started walking on his treadmill.

I said to him, "What do you do all day?"

He said, "I'm in the office all day."

"What do you do at lunchtime?"

"I usually have a protein shake or eat a salad with some chicken."

That's good, I tell him. But I want you to do one more thing. It's easy. While or after you eat, take a walk. Outside. In the parking lot. Once or twice a week.

OK, he says. "But why outside?"

I said, "Sunlight and vitamin D." Then, I told him a story we should all be familiar with by now, which went something like this:

Darker skin is a result of greater production of a pigment called melanin that rewards skin with a natural protection against ultraviolet light. Ultraviolet light would otherwise burn skin, destroy the body's stores of nutrients like folic acid that are needed for refurbishing DNA, increase risk of neural tube defects among other reproductive problems, and also raise risk of skin cancer.

So, in short, melanin is a good thing. Near the equator, with strong UVB rays aplenty to compensate slower vitamin D production, darker skin offers an evolutionary advantage that would only serve to sustain naked humans. But, as often is the case, reward comes with recompense. The downside of higher amounts of melanin is that the pigment interferes with the skin's ability to absorb enough UVB rays to activate Vitamin D's pre-cursor into a full-fledged hormone.
As is well-documented, humans at higher latitudes with dark skin would never have survived over the generations without shedding the extra melanin and opting for a lighter color. Lighter color would afford more UVB absorbed, more D created, stronger bones and, as evidence emerges to show, better cardiovascular health. During summer months, lighter-skinned humans who had migrated to higher latitudes collected vitamin D in fat as they gained weight, then released it into the bloodstream when they shed weight during sunlight-lacking winter months.

On the other hand, when darker-skinned humans live in a Northern latitudes of the United States -- as African Americans do -- you can bet that problems will arise.

Then, I gave him some details about asking his doctor for a 25-hydroxyvitamin D test.

A couple of weeks later, I spotted him outside walking around a parking lot. He tells me, "Thanks so much, David. I had no idea about vitamin D. Plus, my doctor says the walking and the vitamin D are helping my heart."

While attending Experimental Biology (#eb2011) over the weekend, one of the presentations had me thinking about my friend. And that was Richard Harris, Ph.D., of Georgia Health Sciences University in Augusta, presenting a study on vitamin D supplementation in African Americans.

What Dr. Harris and his fellow Georgia researchers found was that vitamin D supplementation in overweight African American adults in a single dose of 60,000 IU every for four weeks every 16 weeks improved blood vessel endothelial function – the equivalent of 2,000 IU since vitamin D has a half life of about three weeks.

It was notable that they used overweight adults, since extra weight can increase blood volume, raise blood pressure, resulting in rigid, inflamed vessels. Details are that the researchers used an inflatable cuff to increase blood flow in the brachial arteries of each of the participants, then an ultrasound to measure flow-mediated dilation.

What exactly vitamin D was able to do is what Dr. Harris calls the "million-dollar question," according to this press release. But it's likely that the hormone acted directly on endothelial cells, on a receptor perhaps, that helps dilate blood vessels when needed. The more dilation, the easier it is for blood to flow through vessels.

This study is great news, especially for this population at higher risk for cardiovascular disease factors like higher blood pressure. However, there is still too little vitamin D deficiency awareness.

Here's what I say, Why not teach African Americans why they have a greater need for vitamin D from an evolutionary perspective?

In the case of my friend, it really helped put things in perspective. There's an easy solution for this mess, which is to take a walk around the block for a few minutes when UVB rays are out (mostly just in summer months) or, simply, by just taking a vitamin D supplement as they did in the summer. Lots of benefits to come from such an easy habit of getting D daily like better blood pressure along with better bone health.

Another thing is that the Institute of Medicine's recommended daily intakes of vitamin D (although they are based as if there were no sun-produced D at all) just make little sense when they don't treat all adults the same, not bringing high-risk groups into consideration. Until more research is available and the IOM can build on current guidelines by raising them for high-risk groups, African Americans should take health into their own hands by getting tested to make sure they keep 25-hydroxyvitamin D in healthy ranges continually.   

1 comment:

eyecandy_babydoll said...

I'm a lil disturbed by all the fuss about supplementing everyone (including other ethnic groups) with vitamin D. Even my relatives in tropical South East Asia (who aren't office workers), have low serum vitamin D. If they lived here, my doctor would nag them to take vitamin D.

Here's why I'm not convinced that Asians and other ehtnic minorities need vit D supplements:

Among descent groups with heavy sun exposure during their evolution, taking supplemental vitamin D to attain the 25(OH)D level associated with optimal health in studies done with mainly European populations may have deleterious outcomes.[14] A review of vitamin D status in India concluded that studies uniformly point to low 25(OH)D levels in Indians despite abundant sunshine, and suggested a public health need to fortify Indian foods with vitamin D might exist. However the levels found in India are consistent with many other studies of tropical populations which have found that even an extreme amount of sun exposure, such as incured by rural Indians,[33] does not raise 25(OH)D levels to the levels typically found in Europeans,[34][35][36]

Another study by the Toronto group[38] did have 'young Canadian adults of diverse ancestry' but applied a standard of serum 25(OH)D levels that was significantly higher than official recommendations.[39]
78% of individuals of East Asian ancestry and 77% of individuals of South Asian ancestry had 25(OH)D concentrations lower than 40 nmol/L. The East Asians in the Toronto sample had low 25(OH)D levels when compared to whites. Lipps (2010)[34] in a world wide review says 'vitamin D deficiency (serum 25(OH)D<25nmol/l) is highly prevalent in China: "A survey in Beijing indicated that Vitamin D-deficiency (plasma 25(OH)D concentration <12.5 nmol/l) occurred in more than 40% of adolescent girls in winter." In a Chinese population at particular risk for esophageal cancer, those with the highest serum 25(OH)D concentrations have a significantly increased risk of the precursor lesion.[11]
In South Asians Harinarayan (2009)[41] found "All studies uniformly point to low 25(OH)D levels in the populations studies despite abundant sunshine in our country". For example rural men around Delhi average 44nmol/L. Healthy Indians living at the latitude they are presumably best adapted to seem have low 25(OH)D levels which are not very different from healthy South Asians living in Canada. South Indian patients with ischemic heart disease have serum 25-hydroxyvitamin D3 levels which are extremely high — above 222.5 nmol/l.[19] The Toronto group conclude -"skin pigmentation, assessed by measuring skin melanin content, showed an inverse relationship with serum 25(OH)D". The uniform occurrence of very low serum 25(OH)D in Indians living in India and Chinese in China does not support the hypothesis that the low levels seen in the more pigmented are due to lack of synthesis from the sun at higher latitudes.

A study[11] found 34% of its sample of healthy western Canadians to be under 40nmol/L at some point and 97% to be under 80nmol/L at least once.
It has been questioned whether to ascribe a state of sub-optimal vitamin D status when the annual variation in ultraviolet will naturally produce a period of falling levels, and such a seasonal decline has been a part of Europeans' adaptive environment[12] for 1000 generations.[13] Still more contentious is recommending supplementation when those supposedly in need of it are labeled healthy and serious doubts exist as to the long term effect of attaining and maintaining serum 25(OH)D of at least 80nmol/L by supplementation.[14]

References can be found here: http://en.wikipedia.org/wiki/Hypervitaminosis_D