R.P.

Smith

et

al.

/

Maturitas

74 (2013) 208–

212

211

serum

hormone

levels

could

be

attributed

to

alterations

in

habitus

and

subsequent

aromatization.

Likewise,

changes

in

physical

activ-

ity

may

account

for

some

of

the

seasonal

variations

seen

in

prior

investigations.

In

their

study

of

915

men

in

San

Diego,

Svartberg

et

al.

found

that

physical

activity

reliably

varied

by

season,

with

a

peak

in

August;

however,

adjusting

for

physical

activity

did

not

change

the

lack

of

seasonal

variation

seen

in

T

[7]

.

The

Svartberg

studies

similarly

evaluated

the

associations

between

seasonal

variations

in

T,

waist

circumference,

and

waist

to

hip

ratio

[14,24]

.

The

authors

found

a

signiFcant

age-adjusted,

neg-

ative

correlation

between

waist

circumference

and

TT

and

±T.

These

hormone

associations

were

stronger

for

waist

circumference

than

for

waist–hip

ratio

or

BMI,

suggesting

that

waist

circumference

may

be

the

anthropometric

measurement

most

reﬂective

of

endoge-

nous

T

levels.

Adjustments

for

BMI

and

lifestyle

factors

diminished

but

did

not

remove

these

associations

[14,24]

.

Waist

to

hip

ratio

followed

changes

in

daylight

and

temperature,

with

peak

values

during

the

summer.

The

lowest

T

levels

occurred

in

months

with

the

highest

temperatures

and

longest

hours

of

daylight,

an

inverse

relationship

with

waist

to

hip

ratio

[14,24]

.

6.

Conclusions

The

studies

reviewed

in

this

manuscript

illustrate

the

het-

erogeneity

present

within

the

literature

in

regards

to

seasonal

variations

of

T.

Limitations

of

these

works

include:

differing

environments

with

wide-ranging

temperatures

and

day–night

patterns;

variable

protocols

for

timing

of

blood

draws;

and

incon-

sistency

in

accounting

for

potential

modiFers

such

as

BMI.

Whereas

some

studies

relied

upon

longitudinal

data,

others

were

only

obtained

from

single

observations.

If

signiFcant

seasonal

variability

of

androgens

exists,

then

it

follows

that

screening

and

laboratory

assessment

of

potentially

hypogonadal

men

and

subsequent

treatment

decisions

would

be

affected.

At

this

time,

recommendations

regarding

timing

of

T

assessment

based

on

seasonal

variations

remain

in

question.

Contrary

to

the

substantial

evidence

for

diurnal

variation

of

T,

reproducible

data

demonstrating

seasonal

patterns

of

T

has

been

more

elusive.

While

some

studies

suggest

its

effects,

others

have

failed

to

replicate

these

results.

The

discussed

inconsistencies

pre-

clude

incorporation

of

circannual

patterns

of

T

into

current

practice

guidelines.

It

can

be

concluded,

therefore,

that

seasonal

variations

of

T,

if

present,

cannot

yet

be

deemed

clinically

signiFcant.

Contributors

Ryan

P.

Smith

M.D.:

Data

acquisition

through

literature

review,

Analysis

and

interpretation

of

data,

Drafting

of

manuscript.

Robert

M.

Coward

M.D.

and

Jason

R.

Kovac

M.D.,

Ph.D.:

Drafting

of

manuscript,

Revisions

for

scientiFc

and

factual

content.

Larry

I.

Lipshultz

M.D.:

Design

and

outline

of

review,

Drafting

of

manuscript,

Revisions

for

scientiFc

and

factual

content,

Super-

vision.

Competing

interests

The

following

authors:

‘Ryan

P.

Smith,

Robert

M.

Coward,

Jason

R.

Kovac

and

Larry

I.

Lipshultz’

declare

no

conﬂict

of

interest.

Funding

The

following

authors:

‘Ryan

P.

Smith,

Robert

M.

Coward,

Jason

R.

Kovac,

and

Larry

I.

Lipshultz’

have

received

no

funding

for

this

article.

Dr.

Kovac

is

supported

by

a

Male

Reproductive

Health

Research

Career

(MHRH)

Development

Program

Physician

Scientist

Award

(K12)

(HD073917-01)

from

the

Eunice

Kennedy

Shriver

National

Institute

of

Child

Health

and

Human

Development

(NICHD).

Provenance

and

peer

review

Commissioned

and

externally

peer

reviewed.

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