Why Do Humans Have Weak Sense of Smell

Compared to nearly all other animals, humans have the weakest sense of smell. You would think that humans and our closest evolutionary cousins (chimpanzees, apes, etc) would have similar sense of smell, but humans still have a much weaker olfactory sense.

Why might that be?

Well, research from Karolinska Institutet have discovered that humans are the ONLY mammals whereby no new neurons are formed in the olfactory bulb after birth. Or if there is any, it is VERY little.

In all other mammals including apes, new neurons are constantly being formed in the olfactory bulb which might explain why all mammals with the exception of humans have a superb sense of smell.

How did scientists figure out the absence of neuron growth in humans?

They looked at Carbon-14 levels within the DNA of the olfactory bulb. Carbon-14 levels in the atmosphere increased significantly due to nuclear bomb testing during the Cold War.

As such, IF new neurons were being formed, one would expect Carbon-14 levels which gets incorporated into developing DNA, to be similar to current atmospheric levels. Or at least find a certain turn-over percentage of both "old" and "new" neurons reflective of the Carbon-14 atmospheric levels at time of neuron development.

However, what researchers have found was Carbon 14 concentrations that corresponded to the atmospheric levels at the time of birth of the individuals establishing that there is very limited, if any, postnatal neuron development in the human olfactory bulb.

Reference:
The age of olfactory bulb neurons in humans. Neuron. May 24, 2012, 10.1016/j.neuron.2012.03.030

Major League Baseball Bans Under the Tongue Deer Antler Spray Use

On Aug 6, 2011, ESPN reported that MLB players have been issued a warning regarding use of Deer Antler spray administered under the tongue.

Deer-Antler spray contains "potentially contaminated nutritional supplements" along with IGF-1 (Insulin Growth Factor) which players have used in the past as an alternative to steroids, especially given it can't be detected in urine samples (only blood testing).

What's with Deer-Antler spray specifically? Scientists discovered IGF-1 in the velvet of immature deer antlers and IGF-1 is considered a performance-enhancer that mediates the level of human growth hormone in the body.

Why under the tongue (sublingual administration)? Because the mucus membrane is quite thin under the tongue richly underlaid with capillary blood vessels allowing for direct diffusion of the substance directly into the body's bloodstream with little or no alteration. This process takes less than a minute to occur. This is in contrast to swallowing a pill which gets digested in the stomach with acid, further digested in the intestines with enzymes, absorbed into the hepatic circulation where further degradation occurs in the liver before getting into general body circulation for effect. A 30-60 minute process.

That's why sublingual nitrogen is such a potent medication to treat chest pain due to an impending heart attack. It works FAST!

It's another reason why sublingual immunotherapy otherwise known as allergy drops is a growing acceptable alternative to allergy shots to try and cure allergies.

Read the ESPN story here.

Tall Women (Over 5'1") Have Higher Risk of Cancer!

Female models may be tall and beautiful, but they are also at markedly increased risk of developing cancer. The New York Times reported on a fascinating research article regarding height of a women and risk of cancer.

Specifically, for every four-inch increase in height over 5 feet 1 inch, the risk that a woman would develop cancer increased by about 16 percent, especially for:

• Colon Cancer (RR per 10 cm increase in height 1.25, 95% CI 1.19—1.30)
• Rectal Cancer (1.14, 1.07—1.22)
• Malignant Melanoma (1.32, 1.24—1.40)
• Breast Cancer (1.17, 1.15—1.19)
• Endometrial Cancer (1.19, 1.13—1.24)
• Ovarian Cancer (1.17, 1.11—1.23)
• Kidney Cancer (1.29, 1.19—1.41)
• Brain/Spine Cancer (1.20, 1.12—1.29)
• Non-Hodgkin's Lymphoma (1.21, 1.14—1.29)
• Leukaemia (1.26, 1.15—1.38)

It is hypothesized that the levels of growth hormone responsible for human height might also be involved in cancer development or because taller people are at greater risk for mutations simply because their bodies are comprised of more cells.

The increased cancer risk was found to be also true across Asia, Europe, Australia, and North America populations.

Perhaps now there's a reason why the average female is 5 feet, 3.8 inches tall! It's a balance between social preferences for being tall versus negative biological consequences for being tall.

The good news here (if there's any) is that head and neck cancer does not increase with height.

Read the NYT article here.

Read the research abstract here.

Reference:
Height and cancer incidence in the Million Women Study: prospective cohort, and meta-analysis of prospective studies of height and total cancer risk. The Lancet Oncology, Volume 12, Issue 8, Pages 785 - 794, August 2011 doi:10.1016/S1470-2045(11)70154-1